USMLE Q Bank Qs Flashcards
An isolate of S. Pneumo from a patient with meningitis is incubated with low-dose radiolabeled ceftriaxone and then subjectedto protein electrophoresis. 5 distinct bands are detected by radioautography. The bandsmost likely represent radiolabeled ceftriaxone that is bound to transpeptidases. An isolate of S. Pneumo from a patient with meningitis is also incubated with low-dose radioactive ceftriaxone and subjected to protein electrophoresis. Only 2 bands aredetected using radioautography. What best explains the observed finding?
Answer: change in protein structure.
Notes: 3 of the penicillin-binding proteins have been altered in such a way that inhibits the binding of ceftriaxone. Structural changes in penicillin-binding proteins that prevent ceftriaxone from binding is one mechanism for ceftriaxone resistance.
*Beta-lactamases function to degrade PCN & cephalosporins. Production of a beta-lactamase would prevent ceftriaxone from being able to bind to the Penicillin-binding proteins. ecause ceftriaxone is so much smaller than the penicillin-binding proteins, unbound ceftriaxone would likely accumulat at one of the electrodes. This would lead to no bands being found within theelectrophoresis area.
A 54 yo male is brought to the ER with a 1-week history of headaches and progressive confusion. He was hospitalized 6 months ago with viral esophagitis and 2 mo ago with pneumocystitis pneumonia. LP is performed and shows a moderate increase in CSF protein concentration and CSF pleocytosis. The latex agglutination test is + for soluble polysaccharide antigen. LM of this patients CSF is most likely to reveal:
Answer: Budding Yeast
Notes: Diagnosis: Cryptococcus Neorofmans. Yeast form only - round or oval encapsulated cells w narrow based buds.
Tx: Amphotericin B & Flucytosine (acute meningitis). Fluconazole for lifelong prophylaxis.
A 28 yo woman comes to the ED w eye irritation and double vision. She also complains of recent weight loss, mood swings, and heart palpitations. Her BP is 140/70 mmHg and pulse is 110/min. Physical examination shows bilateral eye redness and severe proptosis. She is prescribed the appropriate medications and sent home. The patient follows up with her primary care physician 2 weeks later. Her eye symptoms have resolved, and examination reveals a significant decrease in proptosis with no eye redness. The drugthat improved her ocular Sx most likely did so by affecting what?
Answer: Inflammatory infiltration.
Notes: Infiltrative opthalmopathy is characterized by edema and infiltration of lymphocytes into the extraocular muscles and CT. Retro-orbital fibroblasts are then stimulated by cytokines released from infiltratingTH1cells to produce xcessive amounts of glycosaminoglycans. The resulting inflammation and accumulation of glycosaminoglycans increases the volume of the retro-orbital tissues. Dysfunction of the extraocular muscles can also cause restricted extraocular movements and diplopia.
-Severe opthalmopathy is characterized by worsening diplopia, extrocular m involvement, and exposure keratitis. High dose glucocorticois. Glucocorticoids can also prevent worsening of opthalopathy induced by radioactive iodine treatment (esp in smokers). Glucocorticoids can decrease peripheral coversion of T4 to T3 but it is their AI effects that improve theopthalmopathy. Antithyroid drugs do not have a direct effect on opthalmopathy.
A 22 yo caucasian (f) presents to your office with a recent onset of fever & throat pain. Her past medical history is significant for hyperthyroidism controlled with medical therapy. Her BP is 110/70 mmHg and HR is 90/min. PE is insig. What is the best next step in the management of this patient?
Answer: WBC count with differential.
Notes: Diagnosis=agranulocytosis (absolute PMN count of less than 500/mL). Usually occurs within the first few weeks of therpy. Patients typically present with fever & sore throat.
- moa agranulocytosis: AB v circulating PMN.
- **If thionamide-associated agranulocytosis is suspected, the drug is immediately discontinued and a white blood cell count with differential is drawn.
- NB: ASA & ibuprofen are not the best treatments for fever in a patient with thyroid dysfunction because they can displace TH from binding proteins thereby worsening a thyrotoxic state…acetaminophen is preferred!
A 34 yo caucasian female presents to your office complaining of mood swings, difficulty concentrating, and a hand tremor that started only recently. She also admits to having discomfort in her neck. The discomfort radiates to her ears, particularly on swallowing. She ignored the neck & ear discomfort at first because she thought they might be related to flu-like Sx that she had a few weeks ago. Her BP is 140/80 mmHg, and HR is 105/min. You proceeded with a thyroid scan which shows a diffuse decrease in radioactive I uptake. ESR is 105 mm/Hr. Which pathological change in the thyroid gland is most consistent with the clinical sceleraio?
Answer: Mixe, cellular infiltration with occasional multinucleate giant cells.
Notes: Diagnosis=subacute thyroiditis=de Quervain’s thyroiditis = granulomatous thyroiditis.
- PMN–>lymphocyte/histiocyte/multinucleated giant cells.
- thyrotoxic phase–>hypothyroid phase. Self-resolving.
A 52 yo Asian male presents to your office with cough, night sweats, and occasional hemoptysis. Sputum cultures placed on a selective medium grow mycobacteria microscopically observed to grow in parallel chains (“serpentine cords”). This observed bacterial growth pattern most strongly correlates with what?
Answer: Virulence.
Notes: Diagnosis=Mycobacterium Tuberculosis. Serpentine pattern refers to the cord factor - a mycoside (2 mycolic acid molecules bound to the disaccharide trehalose). *The presence of cord factor correlates with vrulence; mycobacteria that do not possess cord factor are not able to cause disease. It inhibits macrophage maturation and releases TNF-alpha. It also inactivates PMN & damages mitochondria.
NB: Sulfatides (surface glycolipids) inhibit phagolysosomal fusion.
A 55 yo, right-handed man comes to the ER department because of recent onset of severe, throbbing, right-sided orbitofrontal h/a and diplopia. His other medical problems include poorly controlled HTN & chronic tobacco use. Neurologic examination shows that he is awake, alert, and orientated and follows both simplex & complex commands. Testing of the CNs reveals intact visual acuity bilaterally. Visual fields and optic fundi are normal. Exam shows anisocoria, with the right pupil being dilated and nonreactive to both light and accommodation. He has evidence of both vertical & horizontal binocular diplopia. The right eye is down and out with ipsilateral ptosis. The rest of the neurologic examination is within normal limits. CT angiography of the head reveals a large aneurysm in the posterior fossa. Diagnosis?
Compressive aneurysm arising from the right posterior cerebral artery. **The 3rd nerve courses between the posterior cerebral and superior cerebellar arteries as it leaves the midbrain and is susceptible to injury from an expanding aneurysm originating from these vessels. *Chronic smoking & poorly controlled HTN are RF for developing intracranial aneurysms.
- GVE periphery (Parasympathetic fibers): pupillary light and near-reflex pathways - more susceptible to injury from ischemia (small-vessel disease due to diabetes mellitus).
- GSE within the interior and subserve the skeletal muscles of the orbit (superior rectus, inferior rectus, medial rectus, inferior oblique, levator palpebrae superioris. More susceptible to injury from a compression.
Diagnosis - non-pupil sparing third nerve palsy on right. Same for compression of posterior cerebral artery & superior cerebellar artery. *Anterior Inferior Cerebellar Artery can compress the facial artery and vestibulocochlear.
A 34 yo male is brought to the ER with severe h/a, blurred vision, hand tremor soon after dining at a local Pizza restaurant. His past medical history is significant for severe atypical depression. His BP is 210/130 mmHg and HR is 110/min. The medication used to treat this patient’s depression is most likely affects waht?
-Answer: enzymatic monoamine degradation.
Notes: This patient is in hypertensive crisis due to couse of MAOi + pizza (cheese - tyramine) - sympathimimetic.
A 36 yo caucasian male presents to your office complaining of periodic involuntary deviation to the right, accompanied by muscle pain in his neck. The spells start spontaneously, last 30-40 minutes, and can sometimes be suppressed by placing a hand on the chin. This patient’s condition can be best characterized as which of the following?
Answer: Dystonia.
Notes: Dystonia - SUSTAINED (v myoclonus) involuntary muscle contractions, which force certain parts of the body into abnormal sometimes painful movements or postures. eg - spasmodic torticollis*, blepharospasm (uncontrollable blinking–>complete closure of eyelids), writer’s cramp.
- Myoclonus: sudden, BRIEF, sometimessevere (shock-like) muscle contraction. Hiccups and hypnic jerks. Pathological myoclonus seen in epilepsy & Creutzfeldt-Jakob disease.
- Chorea: involuntary muscle activity that “flows” from one muscle group to another. Movements may appear fragment or JERKY, and the patient may display a “dancing” gait.
Malignant Hyperthermia
- HSN of skeletal muscles to inhalation anesthetics (esp halothane) & m relaxant succinylcholine.
- Susceptibility AD.
- Defect in Ryanodine R of SR (located on surface of SR of skeletal muscles & is a Ca2+ channel) - relase small amounts of Ca2+ in the cytoplasm of m fiber during m contraction. AbnL ryanodine R releases large amts of Ca2+ after exposure to anesthetic –> ATP-dependent reuptake by SR. Excessive consumption of ATP gnerates heat; loss of ATP along w high T induces m damage. Rhabdoyolysis–>release of K+, Myoglobin, creatine kinase!!!
- Fever, m rigidity. Tachy, HTN, hyperkalemia, myoglobinemia.
- Tx=Dantrolene=muscle relaxant effective in malignant hyperthermia - it acts on ryanodine R and prevents further release of Ca2+ into the cytoplasm of m fiers.
A large, multinational research institute is conducting experiments on human circulatory physiology. The oxygen content of aortic blood is measured in an apparently healthy 35 yo volunteer at rest. Which of the following anatomic sites would normally have a blood O2 content that differs the most from the value obtained from this healthy volunteer’s aorta?
Answer: coronary sinus.
Notes:
1) The heart muscle is perfused during diastole and consumes approximately 5% of CO. Myocardial contraction during systole leads to dompression of the coronary arteries and disruption of BF. Contraction force is highest in endocardium–>severe coronary vessel compression in this area.
2) Myocardial oxygen requirement very high. The heart has a capillary density far exceeding that of skeletal muscle. Oxygen extraction from arterial blood is very effective wtihin the heart: resting myocardium extracts 75%-80% of O2 from blood, while myocardium at work extracts up to 90%.
3) Coronary flow is regulated by local metabolic factors including hypoxia and adenosine accumulation.
Histological evaluation of a portion of GI tract shows ramified, tubular glands located in submucosal layer. The glands contain secretions with pH close to 9.0. Which of the following portions of the GI tract is most likely inspected?
Answer: Duodenum.
Notes:
- Duodenum: villi covered by simple columnar epithelium w BB interspersed with goblet cells & APUD (amine precursors uptake and decarboxylation) cells. Crypts of Lieberkuhn. Brunner’s Glands*.
- Jejunum: villi contain more goblet cells than Duodenum. Lymphocytic infiltration common.
- Ileum like jejunum + peyers patches.
A 21 yo female is taking meds for a recently diagnosed medical problem. While at a college party, she develops facial flushing, h/a, n/v, abd cramps immediately after having an alcoholic drink. The patient is most likely being treated for what condition?
Answer: Trichomonas vaginitis.
Notes: Drug: metronidazole. It’s used to treat trichomonas vainitis and bacterial vaginosis and giardiasis.
- Interaction w alc from inhibition of alcohol oxidizing enzymes, which causes acetaldeyde to accumulate.
- Candida vaginitis is treated w fluconozole.
G+ bacteria are inoculated under the skin of experimental animals and then the infection is treated with antibiotics. Bacteria isolated from the injection site several days later assume a spherical configuration when placed in an isotonic solution and disintegrate rapidly when placed in a hypotonic solution. Which of the following a/b was most likely used in this experiment?
Answer: Cefuroxime.
Notes: G+ has cytoplasmic membrane & peptidoglycan cell wall ouside of that cell membrane. The peptidoglycan cell wallprovides the shape of the bacterium + resistance to osmotic stress*
^PCN, cephalosporin, vancomycin.
A 7 yo patient presents to your office accompanied by his parents. He has been hospitalized multiple times for painful episodes in his hands & feet over the last seeral years. He has no known medical problems and takes no meds except for acetaminophen for pain control. You suspect that he has a valine for glutamic acid substitution at position 6 of the beta-globin chain of the Hb molecule. This patient’s Hb would most likely aggregate upon what?
Answer: Oxygen unloading.
Notes:
- Sickling is promoted by conditions associated with low O2 levels, increased acidity, or low BV (dehydration). - Organs in which blood moves slowly (eg - splen, liver, kidney) are predisposed to lower O2 levels or acidity. In addition, organs with particularly high metabolic demands (eg - brain, muscles and placenta) promote sickling by extracting more O2 from the blood.
- Valine (nonpolar) replaces glutamic acid (+): each chain has several alpha helical stretches (secondary structures) and beta bends (tetiary structure) - substitution of valine for glutamic acid does not result in significant change in beta folding.
- 2-3-DPG binds the 2 beta chains by ionic bonding and stabilizes the taut (T) deoxyHb. TThis binding decreases the O2 affinity of Hb and facilitates the release of O2 at this tissue level. With depletion of 2,3 - DPG, the affinity of Hb for O2 will increase and result in uptake of O2 by Hb. Oxygenated HbS does not polymerize; thus, sickling of erythrocytes will be decreased
During kidney transplantation in a patient with end-stage polycystic kidney disease, the surgeon notices that the graft becomes cyanotic and mottled soon after he connects graft vessel with recipient vessels. The blood flow to the graft eventually ceases and no urine is produced. What is happening?
Answer: AB-mediated HSN.
Notes: Diagnosis=hyperacute rejection of a renal transplant. Usually diagnosed in operating room because the kidney immediately becomes cyanotic & mottled upon anastomosis of the donor & recipient BV and initial perfusion of the organ.
- BF through the new organ ceases immediately due to fibrinoid necrosis of small vessels + rapid formation of extensive thrombosos within the transplanted organ.–>necrosis of the glomeruli & renal cortex, and urine is frequently never produced.
- Hyperacute rejection is an antibody-mediated reaction that is cuased by preformed antibodies within the recipient that are directed against donor antigens. eg - ABO, anti-HLA. T2 HSN.
- Cell-mediated HSN is the immune etiology for acute solid organ transplant rejection & describes the mechanism for T4 HSN.
- GVHD: only occurs in cases where competent donor T-cells are transplanted into a patient who does not possess a functional immune system. Usu in setting of BM transplantation, also in SCID pt receiving blood transfusion w T-lymphocytes. Usu @ skin liver kidney, gut. Diffuse macular eruption @ palms, soles, back, neck. Whole body generalization + bulla formation.
A 57 year old caucasian male is hospitalized with muscle pain, fatigue, and dark urine. His past medical history is significant for stable angina. The patient’s medications include metoprolol, atorvastatin, and ASA. Lab eval reveals that he is in acute renal failure. What med is most likely to have precipitated this patient’s condition?
Answer=Erythromycin
Notes:
- Myopathy is a rare complication of statin use - muscle pain + serum creatine kinase over 10 X the upper limit of normal.
- Erythromycin inhibits cytochrome 3A4. Other macrolides such as clarithromycin also inhibit CYP3A4.
- Other inhibitors of CYP3A4 include ketoconazole, cyclosporine, HIV protease inhibitors, and grapefruit juice.
- If a pt is on an angent that inhibits cyp450 3A4, pravastatin is the statin of choice.
-Acute renal failure is a possible sequela of rhabdomyolysis.
A 21 yo laboratory worker experiences rapid-onset breathing difficulty, palpitations, and flushed skin. He has no significant past medical history and takes only loratadine for seasonal allergies. The patient is suspected to have accidental poisoning. Amyl nitrite from a laboratory safety kit is immediately administered via inhalation. Amyl nitrate affects the affinity of Hb for what?
Answer: cyanide.
Notes:
- Cyanide binds to a variety of iron-containing enzymes, th emost important is cytochrome a-a3 complex.
- CC Cyanide poisoning: rapidly-developing cutaneous flushing, tachypnea, h/a, tachy, often accompanied by n/v, confusion, and weakness, Respiratory distress & cardiac dysfunction may follow. Lab studies indicate severe lactic acidosis in conjunction with a lessenedd difference bw arterial & venous O2 content (the venous blood still highly oxygenated).
- Nitrites oxidize Hb –> Methemoglobin, which can’t carry O2 but binds tightly to cyanide–>dusky discoloration to skin. *Sodium thiosulfate also used for cyanide poisoning - combines with cyanide to form less-toxic thiocyanate, wich is excreted in the urine.
A 35 yo woman comes to the physician because of indurated, painless nodule on her vulva. She has been complaining of occasional h/a and memory loss recently. She has a history of IVDU and multiple sexual partners. Cervical cultures are negative for gonorrhea but a serum VDRL test is positive. LP reveals mild pleocytosis and positive VDRL. What is the vulvar lesion?
Answer: Gumma.
Notes:
1) Primary syphilis: painless ulceration with raised indurated borders (chancre).
2) Secondary syphilis: bacteremic stage of infection and develops 5-10 weeks following resolution of the chancre. Diffuse macular rash that includes the palms and soles. Condyloma lata.
3) Latent syphilis: asymptomatic (early latent within 1 year after resolution of secondary syphilis) and late latent (>1 year).
4) Tertiary syphilis: neurosyphilis (aSx or subacute meningoencephalitis, tabes dorsalis, etc). Ascending aortic aneurysms, aortic valve insuficiency. Gummas - painless indurated granulomatous lesions–>white-gray rubbery lesions and ulcerate. Cutaneous but can be SQ.
* **+VDRL and pleocytosis in CSF diagnositic of neurosyphilis not primary syphilis.
Muscle rigidity is observed in an experiment animal that has chemically-destroyed dopaminergic neurons of the SN. The animal’s rigidity fails to improve with continuous dopamine infusion. Which of the following cell communications account for the lack of responsiveness to dopamine?
Answer: tight junctions.
Notes: Remember that dopamine can’t cross the BBB. C
- Capillaries of the BBB are not fenestrated so paracellular passage of fluid & dissolved material doesn’t occur in CNS. The primary mediators of BBB are tight junctions bw the endotheial cells of CNS capillaries.
- Tight junctions - zonula occludens - claudins & occludens.
Blood cultures from a 54 yo male recently diagnosed with HL reveal motile g+ rods that produce a very narrow zone of beta-hemolysis on sheep blood agar. Which of the following processes is the most important in eliminating these bacteria from the body?
Answer: CMI.
Notes: Diagnosis=Listeria monocytogenes is a g+ rod that produces a very narrow zone of beta-hemolysis on sheep blood agar, similar to the pattern produced by colonies of beta-hemolytic strep. L Monocytogenes shows tumbling motility @ 22C but can be cultured at T as low as 4C. It is a facultative intracellular parasite and the only g+ bacteria to produce LPS endotoxin!!! Listeria can cause serious disease (meningitis, septicemi) in newborns, preg, elderly, immunocompromised.
-CMI stimulates production of cytokines (IFN gamma, TNF-beta, IL-12) that induce a cytotoxic T cell response and macrophage activation and killing of intracellular Listeria.
A 12 yo male is evaluated for ataxia accompanied by episodic erythematous and pruritic skin lesions and loose stools. Laboratory evaluation reveals loss of neutral aromatic amino acids in the urine. This patient’s symptoms would most likely respond to what supplement?
Answer: niacin.
Notes:
- Diagnosis=Hartnup disease: the intestinal and renal absorption of tryptophan is defective. - precursor for nicotinic acid 5-HT, & melatonin.
- CC: aSx, photosensitivity, pellagra-like skin rashes*. Neurologic - ataxia. Neurologic & skin Sx typically wax and wane during the course of this disease.
- The main lab findings in Hartnup disease in aminoaciduria, restricted to the neutral AA (alanine, serine, threonine, valine, leucine, isoleucine, phenylalanine, tyrosine, tryptophan, histidine - branched + aromatic + serine + threonine + alanine). The urinary excretion of proline, hydroxyproline, and arginine remains unchanged, adnd this important finding differentiates Hartnup disease from other causes of generalized aminoaciduria such as Fanconi Syndrome.
- Treatment w nicotinic acid or nicotinamide and high protein diet is okay.
–CC riboflavin deficiency: cheilosis (perleche), glossitis, keratitis, conjunctivitiy,s, photphobia, lacrimation, marked corneal vascularization, seborrheic dermatitis.-B6–>pyridoxal - -phosphate - coenzyme in decarb & transamination of AA. Deficiency–>anemia, peripheral neuropathy, dermatitis.
A 5 yo caucasian male is brought to the ER with somnolence, lethargy, and oliguria. He developed diarrhea several days ago that later became frankly bloody. Lab studies sow elevated blood urea nitrogen & creatinine. Peripheral blood smear reveals fragmented erythrocytes. This patient’s condition is most likely related to consumption of which food?
Answer: undercooked beef.
Notes: Diagnosis=HUS:*: tends to occur most commonly in children under 10 yo and in association with treatment of EHEC gastroeneteritis with a/b.
*Most cases of HUS associated with EHEC O157:H7 have been associated with eating undercooked, contaminated ground beef. Person-to-person contact in families and childcare centers is also an important mode of transmission. Infection can also occur after dinking raw unpasteurized milk & swimming in or drinking sewage-contaminated water.
A 50 yo female presents with abdominal pain, diarrhea, and weight loss. She was diagnosed with DM 2 months ago. Her serum somatostatin level is highly elevated. Further evaluation reveals biliary stones. Suppression of what hormone is most likely responsible for biliary stones?
Answer: Cholecystokinin.
Notes:
-Somatostatin secreted from pancreatic “delta cells” decreases the secretion ofsecretin, cholecystokinin, glucagon, insulin, and gastrin. Present with hyperglycemia or hypoglycemia, steatorrhea, and gallbladder stones.
-Gallbladder stones from bc of poor gallbladder contractility, which is secondary to inhibition of cholecystokinin release.
NB: usually hyperglycemia bc insulin more prfoundly inhibited than glucagon.
^Steatorrhea from decreased secretion of secretin as well as a decrease in GI motility.
^Decrease in gastrin release–>hypochlorhydria.
Ruptured LV free wall
- a complication of ST elevation MI. Days 3-7 after onset of total ischemia. –>cardiac tamponade, which greatly limits ventricular filling during diastole - venous return to heart reduced–>systemic hypoT and pulseless electrical activity. *HypT & SOB. Muffled heart sounds, jugular venous pressure elevation.
- The most common cause of death in patient hospitalized for MI is ventricular F (cardiogenic shock) (2/3).
- *RF ventricular free-wall rupture following MI: >60 yo, female, pre-existing HTN, absence of LV hypertrophy. First MI (previous MIs may be protective bc fibrosis ).
A 45 yo male develops left knee swelling and pain 6 months after a hiking trip to New Hampshire. He has no significant past medical history except for an episode of facial palsy 3 months ago. Which of the following might have prevented this patient’s knee condition?
Answer: Ceftriaxone.
Notes: Diagnosis=Lyme disease caused by spirochete Borrelia Burgdorferi, which is transmitted by the bite of an Ixodes tick. Lyme disease is an endemic in the NE region of the US & N Eu.
*Lyme disease is easily treated with doxy or PCN-type a/b.
A 63 yo male with a recent Hx of MI presents to the ER bc of increasing SOB & cough. PE reveals crackles at the lung bases bilaterally and an S3 on cardiac auscultation. His O2 sat is low. Which of the following most likely accounts for this patient’s dypsnea?
Answer: decrease lung compliance
Notes:
- Dyspnea, bibasilar crackles, and the presence of an S3 sound in a patient w a recent MI suggests L heart F.
- ventricular contractility decrease–>drop in LV output/increase in end-systolic pressure in LH–>impaired diastolic return of blood from pulm–>increasing pressure in pulm veins & capillaries. Increased hydrostatic P in pulm circulation causes transudation of fluid from pulm capillaries into lung interstitioum. *The presence of fluid in the pulm interstitium decreases lung complaince.
- Poor compliance - poor gas exchange since the lungs are not adequately distended.
- Functional residual capacity is increased in diseases that increase lung compliance such as the obstructive lung diseases emphysema and chronic bronchitis. Decreased lung compliance is associated with a decreased FRC.
A 14 yo AA female with sickle cell anemia complains of progressive exertional dyspnea after a minor febrile illness. Lab eval reveals a Ht of 18% & reticulocyte count of 0.5%. Which of the following viruses is most likely responsible for this patient’s current condition?
Answer: non-enveloped single stranded DNA virus.
Notes:
-severe anemia after a minor febrile illness; BM can’t respond appropriately because reticulocyte count not elevated=Aplastic crisis, secondary to parvovirusB19 infection of erythroid precursor cells in the BM.
A 76 yo caucasian female is evaluated for painful lesions on her lips and at the corners of her mouth. She is mildly demented and lives alone. Her urinary riboflavin excretion is very low. Activity of which of the following enzymes is most likely decreased in this patient?
Answer: succinate DH.
Notes:
-rare in US - seen in chronic alcoholics & severely malnourished.
-SS: angular stomatitis, cheilitis, glossitis, seborrheic dermatitis, eye changes (keratitis, corneal neovascularization), anemia.
-Dx via erythrocyte glutathione reductase assay or eval of urinary riboflavin excretion!!!!
-
-Metabolic modifications @ herat, liver, kidney - phosphorylation–>FMN–>FAD. –>reduced, energy-carrying states (FMNH2, FADH2).
*FMN component of complex 1, AD component of complex II - ETC.
-FAD = electron carrier in TCA - cofactor for succinate DH (succinate–>fumarate).
A 34 yo male is an unrestrainedpassenger in a MVA, and sustains considerable trauma. He arrives in the ER hypotensive and bleeding from several sites. As part of the resuscitation efforts, the patient receives a blood transfusion. Abdominal US reveals pslenic laceration & blood int he peritoneal cavity. En route to the operating room for an ER laparotomy, the patient complains of difficulty breathing, chills, and pain in the chest and back. Dark-colored urine is seen draining from the urinary catheter. What is the most likely cause of this patient’s current condition?
Answer: complement-mediated cell lysis.
Notes:
Diagnosis: acute hemolytic transfusion reaction. - in addition to chills, SOB, patients may also experience fever, hypoT, DIC, renal F, hemoglobinuria.
*Acute hemolytic reactions occur within minutes of starting a blood transfusion and are due to ABO incompatibility between the donor & recipient.
*Anti-ABO IC activate C’–>C3a & C5a (anaphylatoxins) & MAC. Anaphylatoxins cause vasodilation & shock, while MAC leads to RBC lysis.
A 21-day-old boy is brought to the office by his mother because of a palpable swelling in the child’s neck. The child continues to feed well but appears comfortable only when held sideways. He is at the 50th percentile for height, weight, and head circumference. he child favors looking toward the right & cries when his head is turned to the left. There is a firm swelling on the left side of his neck that does not move when the child swallows. The remainder of the examination is unremarkable. Which finding is most likely present prenatally?
Answer: Intrauterine malposition.
Notes: Diagnosis: Congenital Torticollis (2-4 weeks of age).
- most commonly caused by malposition of head in utero or birth trauma (bbreech delivery)–>SCM injury & fibrosis.
- Rarely due to cervical spine deformities, C1-C2 subluxation, cervical vertebral fusion. [r/o w cervical spine radiography].
- Additional msk anomalies: hip dysplasia, metatarsus adductus
NB: CONTRACTURE not injury so PE: head tilter toward affected side with chin pointed away from contracture. Soft-tissue mass palpable in inferior 1/3 of affected SCM*. Plagiocephaly (flat head) & facial asymmetry in severe cases.
A 34 yo caucasian male whose older brother died of liver cirrhosis is found to have serum ferritin level of 1800 microgram/L. If the disorder runs in the family, the genetic abnormality primarily affects which of the following processes?
Answer: intestinal absorption.
Notes: -On the short arm of chromosome 6, the hemochromatosis gene (HFE) encodes an HLA class I-like molecule that appears to affect iron absorption from the GI tract. Missense mutation (cysteine-to-tyrosine @ 282). N Eu descent.
A 30 yo male is admitted to the intensive care unit after his wife found him unconscious at home. Lab studies show a serum pH of 7.10 and positive serum ketones. His mucus membranes are extremely dry. The wife notes that he has lost a significant amount of weight recently, despite eating and drinking the normal amounts. Treatment is initiated, and the patient’s pH improves. However, he now complains of fever, h/a, and eye pain. Examination of the nasal cavity reveals black necrotic eschar adherent to inferior turbinate. What procedure would confirm the diagnosis?
Answer: mucosal biopsy.
Notes: Diagnosis: diabetic ketoacidosis … + facial pain + h/a - mucormycosis.
- These fungi proliferate in BV walls, causing necrosis of the downstream tissue. Black necrotic eschar seen in the nasal cavity.
- Histo examination of the affected tissue is necessary in order to make the diagnosis of mucormycosis. : **fungi appear as broad nonseptate hyphae with right angle branchng!!!
- **DDx: aspergillus, which can also affect paranasal sinuses of immunosuppressed patients, causing ismilar Sx. Aspiergillus with SEPTATE hyphae with V shaped branching (45 angle).
A 63 yo female presents to clinic for a routine examination. Her diet consists mainly of fruit & vegetables and she takes a daily multivitamin. Her last menstrual period was 5 years ago. She expresses concern about wrinkles around her eyes that make her “look old.” A decrease in which of the following is most likely responsible for this patient’s complaint?
Answer: Collagin fibril produciton.
Notes:
Human skin exhibits evidence of aging by 30-35 years. : Gradual thinning of epidermis + reduction in SQ fat, BV, hair follicles, sweat ducts, sebaceous glands–>skin to become atrophic/vulnerable.
*Decrease in amt dermal collagen & elastic fiers. No intrinsic reticular support.
A viral protein synthesized in the macrophages of a 22 yo HIV + male is glycosylated and cleaved into 2 smaller proteins in the ER. These newly formed proteins are most likely responsible for which step of HIV infection?
Answer: virion absorption by the target cells.
Notes:
- HIV polyprotein precursurs: gag, pol, env.
- only polyprotein product of the env gene is glycosylated–>gp160…***gp160–>gp120 & gp41 (@ ER, Golgi).
- gp120 mediates viral absorption by binding to the CD4 R of susceptible cells, TM gp41 anchors gp120 through noncovalent interactions, mediating the fusion process bw viruses & target cells.
A 78 yo male inpatient about to undergo bronchoscopy is premedicated with IM atropine & becomes acutely restless, disoriented, and combative. On physical examination, his pupils are widely dilated and non-reactive to light. An EKG monitor shows sinus tachycardia. What drug will reverse ALL of this patient’s Sx & Signs?
Answer Physostigmine.
Notes:
- In elderly > 70 yo, atropine’s t1/2 may be prolonged from its usual 3 hours to up to 10-30 hours due to reduced CL, causing increased susceptibility to toxicity.
- Atropine fever, bronchodilation, tachycardia etc.
- Physostigmine inhibits acetylcholinesterase both peripherally & centrally (tertiary amine)
- Neostigmine & Edrophonium are anticholinesterase drugs too BUT they both have a quaternary ammonium structure that revents penetration of the BBB at moderate doses so would fail to alleviate the patient’s CNS symptoms.
A 43 yo immigrant from Southern Asia suffers from a cough that has lasted for several months duration. He comes to the clinic today because of recent onset hemoptysis. On further eval, he reports a 15-lb weight loss over the past 4 months. Sputum cultures grow acid-fast bacilli that are susceptible to most antimycobacterial drugs in vitro. Isoniazid monotherapy in this patient would most likely result in: ?
Answer: selective survival of bacterial cells secondary to gene mutation
Notes:
*This patient most likely has active TB, which should never be treated with drug monotherapy due to the rapid emergence of antibiotic resistance in M. TB.
*Isoniazid R specifically occurs by 2 selective gene mutations. The first is a decrease in bacterial expression of the catalase-peroxidase enzyme that is required for isoniazid activation once the drug enters the bacterial cell!!! The 2nd mechanism of R occurs through modification of the protein target binding site for isoniazid.
*Tx of active TB: INH + Rifampin + streptomycin, ethambutol, &/or pyrazinamide.
NB: INH monotherapy for PPD+ but negative CXR (no evidence of clinical disease).
A 22 yo male is found to have serum anti-HAV IgG AB although he denies any vaccination against hepatitis. The laboratory findings most likely indicates what?
Answer: an anicteric viral infection in the past.
Notes:
- Most Hep A is silent or subclinical=”Anicteric”=”no jaundice observed”* [acute, self-limited jaundice, malaise, fatigue, anorexia, nausea, vomiting, RUQ pain, aversion to smoking].
- more common in adults. if going to have disease bc less with AB to HAV as living conditions improve!
A leak of radioactive material occurs at a plant that handles the disposal of such waste. A # of workers are believed to have been exposed to this material, which contains heavy isotopes. What should be immediately administered to prevent tissue damage in these individuals?
Answer: Potassium Iodide.
Notes: first step in the formation of thyroid hormone is energy-dependent transport of inorganic iodide into the thyroid follicular cell. “This “Iodide trapping” is accomplished by the sodium iodide symporter. The thyroid follicular cells also take up other ions such as perchlorate and pertechnetate and even radioactive Iodine - so high levels of any one substance will significantly reduce the uptake of the others* - + KI to a person exposed to radioactive isotopes of iodine by competitive inhibition=less radioactive material will enter thyroid, reducing amt tissue damage.
A 56 yo male is admitted to ER with severe chest pain. His initial BP is 240/130 mmHg & HR is 100/min. A BB and nitroprusside infusion is started. Several hours after admission the patient seems confused and disoriented. You noticed that nitroprusside infusion rate is higher than recommended. What needs to be supplied to reverse this patient’s condition?
Answer: Sulfur.
Notes:
- Notriprousside is an antiypertensive with mixed arterial and venous vasodilatory actions. For emergent settings. Given IV continuous infusion and has onset of action within 30 seconds.
- Major disadvantage to use of nitroprusside=potential cyanide toxicity. Nitroprusside is initially metabolized to release cyanide and NO. Cyanide is then metabolized in the liver by “liver rhodanase” to thiocyanite, which is eventually excreted in the urine. - Risk increases with higher dosages, greater infusion rates, prolonged use, and renal insufficiency.
- SS Cyanide toxicity: altered mental status lactic acidosis. Antidote=Sodium thiosulfate. (Cyanide + S=thiocyanite).
A 32 yo female presents to your office complaining of gray vaginal discharge. Wet mount preparations of the discharge reveals moderate leukocytes and numerous squamous epithelial cells covered with adherent bacteria. This patient most likely has an infection with what organism?
Answer: Gardnerella vaginalis.
Notes:
- Diagnosis=bacterial vaginosis usu caused by g variable rod Gardnerella vaginalis. - alterations in the normal vaginal flora (loss of lactobacilli & overgrowth of mixed anaerobic organisms)–>gray discharge & “fishy” odor esp with KOH (“whiff test”).
- Clue cells=vaginal squamous epithelial cells covered in small dark particles (G. Vaginalis organisms).
- Tx: metronidazole (or topical regimens).
Isoproterenol
Adrenergic agonist that stimulates beta 1 (increases HR & CO) and beta 2 R (bronchodilation, decreases peripheral arterial resistance, increase glucagon?).
In an experiment, laboratory animals are subjected to a toxic insult that specifically targets the protein kinesin. What is most likely to be absent from tissues on histological examination?
Answer: secretory vesicles in nerve terminals.
Notes: kinesin=microtubule associated motor protein whose function is anterograde transport of intracellular vesicles and organelles toward the plus (rapidly growing) ends of MT. It uses energy derived from ATP hydrolysis to move along the microtubule.
