Repro USMLE step 1 9-5 (7)

Question 1

This female infant presents with ambiguous genitals, hypotension, and signs of dehydration and electrolyte disturbances, including a low bicarbonate concentration, hyponatremia, and hyperkalemia. This indicates that this infant has congenital adrenal hyperplasia, most likely occurring secondary to 21-hydroxylase deficiency. This patient lacks enzymes necessary to convert steroid precursors to aldosterone or cortisol, leading to hypotension and the electrolyte disturbances indicated by her test results. Patients with 21-hydroxylase deficiency will have an?

Answer 1

accumulation of serum 17-hydroxyprogesterone, its substrate. The excess substrate is shunted to androgen production, leading to virilization. 21-Hydroxylase deficiency is the most common cause of congenital adrenal hyperplasia.

Question 2

The other answer choices would not present with this clinical picture. Decreased plasma renin would be contrary to a presentation that includes hyponatremia; the renin concentration would be elevated in compensation. Decreased serum dehydroepiandrosterone (DHEA) suggests a lack of excess androgens, but this female infant has virilization of her genitals, which indicates an elevated level of androgens. Androgens include DHEA, androstenedione, and testosterone—some of which are steroid precursors. Accumulating steroid precursors in 21-hydroxylase deficiency are driven toward ?

Answer 2

the production of excess androgens. Even in patients with 3ß-hydroxysteroid dehydrogenase deficiency, DHEA levels remain elevated despite low levels of androstenedione, causing some degree of virilization. Elevated serum 11-deoxycorticosterone is found in patients with 11ß-hydroxylase deficiency. However, salt wasting would not occur in a patient with 11ß-hydroxylase deficiency, and hypotension would not commonly be seen. Elevated serum cortisol would not be possible in a patient with congenital adrenal hyperplasia, given the deficiency in enzymes required for its synthesis.

Question 3

Female patients with 21-hydroxylase deficiency, the most common cause of congenital adrenal hyperplasia, present with virilized genitals and hypotension, along with hyperkalemia and hyponatremia caused by renal salt wasting. These patients also have an elevated level of?

Answer 3

serum 17-hydroxyprogesterone.

Question 4

This patient’s single painless chancre/papule with a firm base on the vulva and her positive Venereal Disease Research Laboratory (VDRL) test are indicative of a diagnosis of primary syphilis. Syphilis is caused by the spirochete Treponema pallidum.
Often, the painless chancre of the primary phase of syphilis will heal on its own without any intervention; this does not indicate that the infection has been eradicated by the immune system, only that the primary phase of infection has ended. In the diagnosis of syphilis VDRL positivity in conjunction with a positive FTA-Abs test is indicative of active infection. The treatment of choice for primary syphilis is?

Answer 4

benzathine penicillin G which acts by binding bacterial transpeptidase proteins and preventing the cross-linking of peptidoglycan within the bacterial cell wall. Furthermore, penicillin is safe for use in pregnancy. Treatment of syphilis is particularly important in pregnant women since congenital syphilis can result in severe damage to the fetus, causing stillbirth, deafness, and physical findings including notched teeth, a saddle nose, and saber shins.

Question 5

Amoxicillin and penicillin V are oral β-lactam agents that are not indicated for?

Answer 5

the treatment of syphilis. Azithromycin is indicated for the treatment of Chlamydia infection and chancroid caused by Haemophilus ducreyi. Doxycycline and ceftriaxone are commonly used to treat Chlamydia infections and gonorrhea.

Benzathine penicillin G is considered the first-line treatment for syphilis.

Question 6

Primary syphilis presents with a single, painless chancre/papule with a firm base and is treated with?

Answer 6

intramuscular penicillin G.

Question 7

This patient has left lower abdominal pain, nausea and vomiting. The results of her physical examination and pregnancy test confirm that she is pregnant, and further surgical investigation proves that it’s an ectopic pregnancy. Ectopic pregnancy refers to extrauterine locations of the fetus. An ectopic pregnancy may be tubal, abdominal, or intraligamentous (broad ligament). Risk factors for ectopic pregnancy include previous history of pelvic inflammatory disease, prior ectopic pregnancy, tubal pelvic surgery, and exposure to teratogens.
In order of decreasing frequency, tubal pregnancies most commonly occur in?

Answer 7

the ampulla, isthmus, fimbriae, and interstitium, as illustrated in the image. The other choices portray an incorrect order.

Question 8

This otherwise healthy woman presents with a 2-month history of abdominal fullness, an ovarian mass, ascites (which manifests as a fluid wave), and hydrothorax (pleural effusion) demonstrated by her decreased breath sounds. This triad is the classic presentation of Meigs syndrome, which is caused by a benign ovarian fibroma. It is important to note that unlike other stromal cell tumors, the fibromas associated with?

Answer 8

Meigs syndrome do not secrete sex steroid hormones. The classic histology of a fibroma shows collagen-rich spindle cells, as seen in this patient’s biopsy specimen.

Question 9

The triad of an ovarian mass, ascites, and hydrothorax is not seen in patients with the following types of masses:

dermoid cyst, usually a benign ovarian tumor that is primarily found in women in their twenties and thirties

endometrioma, cystic ovarian mass filled with blood and resulting from?

Answer 9

ovarian endometriosis

struma ovarii, a specialized, monodermal teratoma composed entirely of mature thyroid tissue

Moreover, these ovarian masses are not composed of spindle cells and collagen.

Question 10

Meigs syndrome is the triad of benign ovarian tumor, ascites, and hydrothorax (pleural effusion). The classic histologic finding in a Meigs syndrome tumor is ?

Answer 10

the presence of collagen-rich spindle cells.

Question 11

This woman is 15 weeks pregnant, and her physician is able to tell her the sex of her baby based on ultrasound findings. Dihydrotestosterone (DHT) is produced from testosterone by the enzyme 5a-reductase. It is three times more potent than testosterone. Prenatally, DHT is responsible for?

Answer 11

the formation of male external genitalia. Later, it is involved in the development of secondary sexual characteristics such as hair distribution, increased stature, and increased sweat gland secretion. DHT also causes an increase in the size of the epididymis and prostate.

Question 12

Androstenedione is a weak androgen that does not significantly contribute to?

Answer 12

male external genitalia development. Testosterone itself is involved in male internal genitalia development. FSH and progesterone are not involved in the formation of external genitalia.

Question 13

DHT is required for the formation of normal male external genitalia in utero. The differentiation of male internal genitalia is driven by?

Answer 13

testosterone.

Question 14

The patient presents with an eczematous lesion on the left nipple and a burning sensation in the breast with no systemic symptoms. The biopsy histology is marked by the presence of large cells surrounded by “halos”. This is most consistent with?

Answer 14

Paget disease of the breast, which is a form of breast adenocarcinoma involving the skin and lactiferous sinuses of the nipple.

Paget disease of the breast is most often associated with excoriations, crusting, ulceration, and serosanguineous discharge. The disease is identified on histology by the presence of large cells with clear cytoplasm surrounding a hyperchromatic nucleus. These cells are known as Paget cells ( the clear cytoplasm is frequently referred to as a “halo”) and can be found throughout the epidermis in this disease. Although the disease can manifest at anytime, it is most commonly diagnosed in the fifth decade. Paget disease of the breast is almost always associated with an underlying invasive ductal carcinoma. There are four clinical stages of Paget disease of the breast. The prognosis is related to the stage of disease, as in other types of breast cancer.

Question 15

The other answer choices are not consistent with this patient’s presentation. Invasive lobular carcinoma often presents bilaterally and usually does not form a distinct mass. Intraductal papilloma typically presents with bloody nipple discharge but without skin changes. Mastitis is an infection which is commonly associated with?

Answer 15

breastfeeding and has systemic symptoms like fever and chills. Phyllodes tumors present as firm, multinodular, painless masses that can grow large enough to distort the skin but do not cause the changes seen in this patient.

Question 16

Paget disease of the breast appears as an eczematous lesion of the nipple, often associated with excoriations, crusting, ulceration, and serosanguineous discharge. Histology shows large cells with clear cytoplasm surrounding a hyperchromatic nucleus. Paget disease of the breast is almost always associated with?

Answer 16

an underlying invasive carcinoma.

Question 17

This patient, who presents at 16 weeks’ gestation, has no obvious symptoms, but routine quadruple screening test results show elevated a-fetoprotein, which is indicative of ?

Answer 17

an “open” (ie, not skin covered) neural tube defect (NTD), such as meningocele, myelomeningocele, encephalocele, or anencephaly. This patient’s levels of inhibin, estriol, and ß-hCG are normal. The open NTD allows the leakage of both a-fetoprotein and acetylcholinesterase to occur. However, a-fetoprotein can cross the placenta and therefore is detected in the maternal serum according to quadruple screening test results.

Open NTDs usually result from defective primary neurulation, whereas closed NTDs are the result of defective secondary neurulation.

Question 18

The exact cause of an NTD is unknown and is likely multifactorial; factors may include radiation, drugs, malnutrition, and genetics. Maternal folic acid supplementation reduces the risk for NTDs. However, some medications reduce or inhibit production of folic acid, including valproic acid and methotrexate. The major NTDs include?

Answer 18

spina bifida occulta, meningocele, myelomeningocele, encephalocele, and anencephaly. Note that in spina bifida occulta, the a-fetoprotein level can be normal or elevated.

Question 19

Abnormal conception leading to excessive trophoblastic development, which is diagnostic for gestational trophoblastic disease, presents with characteristically elevated serum ß-hCG, not a-fetoprotein. Full or partial trisomy 18 is suggested in quadruple screening test results by decreased a-fetoprotein, decreased estriol, and decreased ß-hCG. Nondisjunction in maternal gametes, indicative of?

Answer 19

trisomy 21 or Down syndrome, is suggested in quadruple screening test results by decreased a-fetoprotein, decreased estriol, increased inhibin A, and increased ß-hCG. Splitting of the fertilized ovum 2–12 days after fertilization would indicate twins, based on quadruple screening test results of increased a-fetoprotein, increased estriol, and increased ß-hCG.

Question 20

Elevated α-fetoprotein levels in maternal serum during gestation are associated with “open” (ie, not skin covered) NTDs, such as meningocele, myelomeningocele, encephalocele, and anencephaly. Normal α-fetoprotein levels are found with spina bifida occulta. NTDs can often be prevented with?

Answer 20

adequate maternal intake of folic acid.

Question 21

This patient presenting with vaginal bleeding and a placenta encroaching over the cervical os is most likely suffering from placenta previa, or the attachment of the placenta to the lower uterine segment. Placenta previa typically manifests with painless vaginal bleeding after 20 weeks of gestation. Risk factors include history of a prior cesarean section delivery, increased number of pregnancies, twin gestation, and history of curettage. Ectopic pregnancy, on the other hand, most commonly occurs in the first trimester and is characterized by?

Answer 21

vaginal bleeding and/or abdominal pain. This pregnancy also has evidence of a gestational sac and intrauterine heartbeat.

Question 22

History of endometriosis leads to increased risk of infertility and epithelial ovarian cancer. History of pelvic inflammatory disease (PID) leads to an increased risk of ectopic pregnancy and is often associated with infertility. Prior ectopic pregnancy leads to?

Answer 22

an increased risk for future ectopic pregnancies. Use of assisted reproductive technologies leads to an increased risk for multiple gestations.

Question 23

Placenta previa, or the attachment of the placenta to the lower uterine segment, typically manifests as ?

Answer 23

painless vaginal bleeding after 20 weeks of gestation. Risk factors include prior cesarean section delivery, increased number of prior pregnancies, twin gestation, and a history of curettage for spontaneous or elective abortion.

Question 24

This young man presents with a painless testicular lump that has no clear etiology. Taken in combination with findings of a nontender, homogenous right testicular enlargement on ultrasound and enlarged para-aortic lymph nodes on abdominal CT, the differential diagnosis includes?

Answer 24

testicular cancer with possible metastasis. Seminomas are the most common type, accounting for approximately 40% of testicular cancers. Seminomas are most often diagnosed in men between the ages of 25 and 40 years and do not occur in infancy. Because the testicles drain to the para-aortic lymph nodes, lymphatic spread of testicular cancers is often seen in the para-aortic chain. Patients with seminomas will typically have an elevated level of placental alkaline phosphatase (tumor marker).

Question 25

Epididymitis and torsion of the appendix testis would both present with pain and would not cause para-aortic lymphadenopathy. Leydig cell tumors present with signs of hyperandrogenism, which are not present in this patient, and yolk sac tumors are usually found in children under the age of 4 years. Embryonal carcinoma is another type of testicular tumor, which presents as a?

Answer 25

hemorrhagic mass with necrosis, but a “pure” embryonal carcinoma is rare.

Question 26

A seminoma is the most common type of testicular cancer in men aged 25 to 35 years and typically presents with a unilateral, hard testicular mass and testicular pain or a “dragging sensation.” Testicular tumors will often drain and metastasize to the para-aortic lymph nodes. Patients with seminomas will typically have an?

Answer 26

elevated placental alkaline phosphatase (tumor marker) level.

Question 27

A healthy woman who presents to the physician is concerned about inheriting breast cancer because of a family history of breast and ovarian cancer. The BRCA1 and BRCA2 genes are strongly associated with breast cancer. BRCA is an example of a tumor suppressor gene. A mutation results in loss of function, and thus both alleles must be lost for development of cancer. The BRCA1 and BRCA2 genes are found on chromosomes 17 and 13, respectively.

This patient’s family history is suggestive of a BRCA1 mutation because it is more strongly associated with ovarian cancer than BRCA2, although patients with BRCA2 mutations are also at an increased risk for ovarian cancer compared with the general population. Chromosome 17 is also the source of?

Answer 27

the NF1 gene mutation in neurofibromatosis type 1, which is an autosomal dominant disease characterized by cafe-au-lait spots, Lisch nodules, and neurofibromas. A useful hint to remember this by is the word “Neurofibromatosis,” which has 17 letters, therefore NF1 occurs due to a mutation on chromosome 17. Because BRCA1 and NF1 are both found on chromosome 17, neurofibromatosis type 1 is the correct answer.

Question 28

The APC gene, which is responsible for causing familial adenomatous polyposis, is found on chromosome 5. The NF2 gene, which causes neurofibromatosis type 2, is found on chromosome 22. The genes DCC and DPC are implicated in colon and pancreatic cancers, respectively, and are both found on ?

Answer 28

chromosome 18. The VHL gene results in von Hippel-Lindau syndrome and is found on chromosome 3. The WT1 gene, which causes Wilms tumor, is found on chromosome 11.

Question 29

The most common inherited forms of breast cancer result from a mutation that knocks out the BRCA1/BRCA2 tumor suppressor genes located on chromosomes 17 and 13, respectively. Chromosome 17 is also the source of the NF1 gene mutation in ?

Answer 29

neurofibromatosis type 1.