Clinical Correlations Flashcards
What causes meralgia paresthetica?
Pressure on the Lateral Femoral Cutaneous N. (L2,3)
What are the symptoms of meralgia paresthetica?
Variable temperature sensations in the thigh
Describe the pathological progression of ischial/throchanteric bursitis
Friction bursitis pathologic progression: fluid filled spaces, friction rub, inflammation, fibrosis, ca++ deposits, rupture of bursa or associated tendon
Describe creatine kinase
An enzyme (three isoforms, found in the heart, brain, lung & skeletal muscle) which catalyzes the conversion of phosphocreatine + ADP → ATP (it also does the reverse rxn). Increased serum CK is an indication of; MI, rhabdomyolysis, muscular dystrophy, myasthenia gravis, myositis, acute renal failure, and certain drug use (Acronym = “MRDRD)”.
Carnitine Deficiency Syndrome
Several etiologies, and symptoms can be dynamic. Primary = defective carnitine transporter, so FA can’t get past the outer mitochondrial membrane. Secondary = Carnitine inaccessible because it cannot be removed from acyl group, (eg a problem with CPT-II). The result is a significant reduction of beta-oxidation
Describe Fatty Acid Transport Defects
Several etiologies (eg deficiency in CPT I (on inside of outer membrane), CPT II (on inside of inner membrane), or a defect in carnitine/acylcarnitine translocase). Also results in a significant reduction of beta-oxidation.
Defects of beta-oxidation (Mitochondrial) enzymes
Most present with myopathic symptoms or signs that are usually progressive, but dynamic symptoms may also be observed (Recall that long-chain FAs represent a major source of energy for prolonged, low-intensity exercise lasting more than 40-50 minutes.
Describe AMP deaminase deficiency
The enzyme which converts 2 AMP → ATP + IMP + NH3. Deficiency of this enzyme is a common cause of exercise-induced myopathy, and probably the most common cause of metabolic myopathy in humans.
+ EMG and - NCV indicates what?
Myopathy
+ EMG and + NCV indicates
Neuropathy
Describe myasthenia gravis
Immune mediated loss of Ach receptor → decreased ability to generate an end-plate potential → muscle weakness. Although nerve conduction is normal, motor response diminishes after repeated stimulation. 9
What percentage of patients show opthalmological manifestations of myasthenia gravis? What are the manifestations?
90%
Ptosis, blurred vision and general weakness
What worsens the symptoms of myastenia gravis?
Increased activity worsens fatigue and weakness
What can be used to treat myasthenia gravis? How does it work?
Edrophonium/Tensilon (an acetylcholinesterase inhibitor), which inhibits the breakdown of Ach, thus allowing ACh to accumulate in the NMJ.
[Ach] ↑ at the muscle end plate -> increased muscle strength. Application of ice packs also slows AChE enzyme, so it provides similar (but short term) effects to patients presenting with ptosis.
What is the mechanism behind Lambert–Eaton myasthenic syndrome (LEMS, a paraneoplastic syndrome)?
mmune mediated attack directed against voltage-gated calcium channels (VGCCs) on the presynaptic motor nerve terminal → loss of functional VGCCs → Ca-mediated exocytosis is greatly diminished.
What is a noteable difference between myasthenia gravis and Lambert–Eaton myasthenic syndrome?
Unlike myasthenia gravis, repeated stimulation → enough Ca-influx via functioning channels to trigger synaptotagmin (T-snare) → exocytosis of ACh-containing vesicles.
How do tetanus and botulinum toxins function? Symptoms?
hether Tetanus or Botulinum, these neurotoxin endoproteinases target the snare complex. Whether they target V-snares or T-snares, fusion of ACh-containing vesicles is blocked → dry mouth, double vision, difficulty swallowing and speaking, vomiting and diarrhea (Botox)
Hyperkalemic Periodic Paralysis is an utosomal dominant trait which affects the skeletal muscle gene SCN4A, located on chromosome 17. What is the mechanism of action?
This mutation impairs fast-inactivation of voltage-gated Na+ channels → Small, persistent influx of Na+ → Depolarizes the membrane → hyperexcitability.
What clinical symptoms are associated with hyperkalemic periodic paralysis?
Clinically, severe muscle myotonia, weakness and/or paralysis are observed during a period of rest AFTER exercise, stress, fasting, or ingestion of large amounts of K+ (eg bananas).
Malignant Hyperthermia - a rare, autosomal dominant trait, which results in a defective __________.
RYR1 gene, impacting ryanodine on the sarcoplasmic reticulum membrane.
Describe malignant hyperthermia
his disorder of Ca regulation in skeletal muscle → uncontrolled release of Ca2+ from the SR → rigidity, tachycardia, hyperventilation, and hyperthermia & acute hyper-metabolic state within muscle tissue (prolonged contraction). MH can be triggered by volatile anesthesia and muscle relaxers, resulting in a potentially fatal increase in body temperature.
Describe Multiple Sclerosis
A T-cell mediated autoimmune disorder, in which myelin in CNS (produced by oligodendrocytes) is attacked by one’s own immune system.
Trigger and age of onset of MS? What neurons are impacted? What is the lost myelin replaced with?
Trigger is unclear, middle age onset.
Both sensory and motor neurons impacted.
Scar tissue, substantially reducing conduction velocity
What often worsens MS symptoms? Conversely, what often improves them?
Symptoms in patients with M.S. are often worsened with increased body temperature, which affects the gating kinetics of voltage-gated Na+ channels. Treatments include cooling temperature and K+ channel blockers (which slow the repolarization phase, and prolong the AP)
How do local anesthetics function?
Inhibits VG Na+ channels, thus conduction of APs in the axon
How does Tetrodotoxin (puffer fish poison) function?
Works essentially the same as local anesthetic, high doses → muscle paralysis (including paralysis of the diaphragm)
How do Acetylcholinesterase Inhibitors (Rx name is Edrophonium/Tensilon) work? What are some uses?
revents the recycling of Ach from the synapse.
Used to treat Myasthenia gravis, and sometimes dementia (Alzheimer’s or Parkinson’s) but not as effective. Also used as a chemical weapons.
Describe Curare Alkaloids
A class of drugs which are neuromuscular blocking agents. Used for causing muscle paralysis during anesthesia. It is a competitive antagonists that targets the nACh receptor, and so DOES NOT allow depolarization → paralysis
How does Succinylcholine work?
Also a neuromuscular blocking agent, used for causing muscle paralysis during anesthesia. It is an agonist which targets the nACh receptor and so DOES allow depolarization. It’s first action is to initially bind & open the channel, but with subsequent APs → receptor is occupied by succinylcholine → paralysis.
What does dantrolene do? What is it used to treat?
Inhibits the RYR receptors on the SR membrane, thus blocking the release of Ca2+ from SR, so no muscle contraction. Used to treat malignant hyperthermia and spasticity associated with upper-motor neuron disorders.
Describe the cause and appearance of the Trendelenburg Gait
The abductor muscles (gluteus medius and minimus) are weak, and so allow pelvis to rock to the side, resulting in a “waddling” gait. The patient leans towards the side which has lost the ability to abduct. Most often is a problem with the superior gluteal nerve, but can also be a problem with the muscles themselves.
What is Gower’s sign, and what causes it?
Due to a lack of hip and thigh muscle strength, the patient must use their hands and arms to “walk” up their own body from a squatting position.
Describe Rhabdomyolysis. What organ can be impacted by this?
he breakdown of muscle fibers → muscle fiber contents (myoglobin) released into the bloodstream. These globular proteins get caught in the glomerular heads of the kidney → Kidney failure
Duchenne Muscular Dystrophy - An x-linked recessive condition, though many cases are due to spontaneous mutations. Describe the pathology of this disease.
he costameres, which ties the muscle cell membrane to the filaments, and contains the protein dystrophin. When dystrophin function is lost, the result is an inability to transmit the force to the cell membrane, and thus the ECM. Increased Ca2+ influx, which leads to oxidative stress, and ultimately necrosis of the myofiber. myofibers are then replaced by CT and adipose. In short, you lose dystrophin function, and so can’t transmit force outside of the cell → muscular atrophy.
What causes ischial bursitis? When is this bursa weight bearing? What scenario is this often seen in clinically?
Caused by movement of the gluteus maximus across the bursa overlying the ischial tuberosity. Also note that this bursa is weight bearing while seated. Bursa may become calcified, and with prolonged bedrest → pressure sores and ulceration
What causes Trochanteric bursitis? Where does the pain radiate to? What muscles put pressure on the trochanteric bursa?
Caused by movement of the gluteus maximus across the bursa overlying the greater trochanter (eg climbing or inclined walking). Causes pain which radiates deeply inferiorward from posterior the bursa along the lateral thigh to the knee. Recall that both the gluteus maximus and the tensor fascia lata insert onto the IT band, so activity of either muscle (tensor fascia lata during flexion, and gluteus maximus during extension) put a constant pressure on the trochanteric bursa.
Other common sites of bursitis?
iliopectineal, infra-, supra-, and prepatellar bursitis, retinacular bursitis, and calcaneal bursitis
Describe Medial Plantar Nerve Compression
analogous to CTS, as this nerve also passes under a flexor retinaculum. Excessive running or eversion → irritation of this nerve → paresthesias on the medial side of the sole of the feet, with weakness of the intrinsic muscles of the great toe.
What is the cause of plantar fasciitis? How about the pathology? What can be the long term result? How does one test this?
Plantar aponeurosis becomes inflamed (eg overuse, running, high impact activities). Pain can be elicited by; direct pressure at the point of its attachment to the calcaneus, by dorsiflexion, or by extending the great toe. It is often accompanied by calcaneal bone spurs in the direction of the aponeurosis and the surae muscles.
Describe femoral hernias
Viscus contents (a portion of the gut) protrudes through the femoral ring into the femoral triangle. May even protrude through the saphenous opening, in which case venous return of the greater saphenous vein would be impeded. Occurs more often in females.
How does compartment syndrome arise? How does it present clinically? What is necessary to relieve the symptoms in extreme cases?
Pressure increases within a fascial compartment, which can reduce blood flow, impinge nerves (causing distal paresthesias or paralysis of muscles within that compartment). Severe cases require fasciotomy to relieve these compressive forces prior to the occurrence of tissue necrosis.
How do muscular strains and ruptures typically occur?
Most often occurs as a result of large muscles exerting force quickly to overcome large amounts of inertia. AS lower limbs are weight bearing, this may occur during sprints, rapid change in direction, etc → injury close of the site of attachment.
What muscles are involved in groin strains, and how does the damage occur?
Adductor group “pulls” usually during fast hip-flexion activities.
What is the usual cause of hamstring strains?
Hamstrings strain near the ischial tuberosity as a result of fast extension during the “push-off” phase of running.
Describe Ruptured Achilles Tendon injuries
Week-end warrior injury”, due to increased age and irregular bouts of exercise (eg tennis or basketball) where rapid push-offs with the feet are required.
What would be used to evaluate a ruptured achilles tendon?
Sagittal MRI
Describe the cause of psoas abcesses. What misdiagnoses are common with this?
s a result of a retroperitoneal abdominal or pelvic infection that descends within the psoas sheath, deep to the inguinal ligament → pain and swelling w/in the femoral triangle, which can put pressure on the femoral nerve. This is often misdiagnosed as a femoral hernia, indirect inguinal hernia, inflammation of the inguinal lymph nodes, or a saphenous varix.
Describe Tibialis Anterior Strain (“Shin Splints”)
Microtears in the periosteal attachment (sharpey’s fibers) of the distal ⅔ of the tibialis anterior muscle to the tibia → pain. Also, decreased vascular exchange → swelling and inflammation within the muscle → pain. Usually results from overuse, infrequent bouts of exercise preceded by not stretching or warming up first and/or running on hard surfaces after having trained on softer surfaces.
What is the cause of calcaneal tendinitis? What is the pathology behind it?
Micro tears in the attachment of the calcaneal tendon to the calcaneal tuberosity. Occurs as a result of overuse, poor footwear, poor training surfaces, or infrequency of activity.
Describe a bipartite or tripartite patella
Asymptomatic non-union of the ossification centers of the patella. Often is misinterpreted as a Fx.
What is this fx?
Stress Fx (March Fx)
What is this image showing
Osgood-Schlatter Disease
What’s going on in these images? Describe the condition?
Slipped Capital Femoral Epiphysis
Due to trauma in the region of the proximal femoral epiphysis (usually occurs in adolescents prior to epiphyseal plate closure). Distal fragment dislocates posteriorly → coxa vara
Describe Avascular Necrosis of the Femoral Head
Due to disruption of the arteries that surround the femoral neck and provide branches to the femoral head (branches of the medial femoral circumflex artery are most often implicated).
How does one test for ACL Vs. PCL
What’s going on in these images? Describe the condition!!!!
Chronic knee joint effusion (fluid accumulation) in the joint moves into the bursae. Occurs most often posteriorly (in the gastrocnemius or semimembranosus bursa). May impede flexion or put pressure on structures in the popliteal fossa → pain
Gluteal Injections
Glut injections should be administered between the index finger (placed on the ASIS) and the the middle finger (placed on the tubercle of the crest of the ilium). Injections done inferior to this area could damage the Sciatic N.
