Free STEP1 Exam Braindumps

A 2-year-old male patient develops progressive generalized weakness and muscle atrophy. The impairment first began with the muscles of the hips, and then progressed to the pelvic area, thigh, and shoulder muscles. The patient is diagnosed with Duchenne's muscular dystrophy, a congenital disorder where the protein dystrophin is deficient. Which of the following describes the role of dystrophin in muscle tissue?

  1. anchors actin to the sarcolemma
  2. endows the myosin filaments with elastic recoil properties
  3. extends from Z disk to Zdisk, forming a supportive network
  4. inhibits the binding of myosin to actin
  5. protects desmin filaments from stressinduced damage

Answer(s): A

Explanation:

Dystrophin anchors actin to the sarcolemma, reinforcing and stabilizing the latter during muscle contraction. Titin is a large protein which associates with myosin filaments and endows them with elastic recoil properties (choice B). Desmin filaments form a supportive network extending from Z disk to Zdisk (choice C). Troponin I inhibits the binding of myosin to actin (choice D). AlphaB-crystallin protects desmin filaments from stress-induced damage (choice E).



A 27-year-old woman who recently delivered her first child develops an infiltrative mass in the anterior abdominal wall. A biopsy reveals sweeping fascicles of well-differentiated, plump monomorphic fibroblasts that infiltrate surrounding tissues. Based on this information, what is the most likely diagnosis?

  1. desmoid tumor
  2. fibrosarcoma
  3. malignant fibrous histiocytoma
  4. myositis ossificans
  5. nodular fasciitis

Answer(s): A

Explanation:

Desmoid tumors are mesenchymal tumors that are locally aggressive but do not metastasize and have a benign microscopic appearance characterized by well-differentiated fibroblasts. Those tumors arising in the anterior abdominal wall are usually seen in women who are pregnant or recently postpartum.
Fibrosarcomas (choice B) are rare malignant mesenchymal tumors that can metastasize and would typically be expected to have a more pleomorphic microscopic appearance (often with a "herringbone pattern") than that seen in desmoid tumors. Malignant fibrous histiocytomas (choice C) are also malignant mesenchymal tumors that would have a pleomorphic microscopic appearance. Myositis ossificans (choice D) is a non-neoplastic lesion that often forms following blunt trauma to muscle in a lower limb. The initial hematoma undergoes organization with calcification and can have a pleomorphic appearance with numerous mitoses, leading to the possibility of a misdiagnosis as a malignancy. Of special note, however, is that the bone in myositis ossificans matures from the periphery to the center, whereas the opposite pattern is seen in a malignant tumor. Nodular fasciitis (choice E) presents as a rapidly growing, potentially painful mass that may occur in association with prior trauma. Its histological appearance can be worrisome and, similar to myositis ossificans, may lead to misdiagnosis as a malignancy (sarcoma) as it is somewhat pleomorphic with immature fibroblasts and many mitoses. However, these lesions are self-limited and excision is curative.



A 72-year-old woman was hospitalized after becoming acutely ill. Despite intervention, she died 9 days later. One of the findings at her autopsy is shown in below figure which is a section of her left kidney. Which of the following conditions could have led to the changes seen in this patient's kidney and was most likely the reason for her hospitalization?

  1. MI
  2. pyelonephritis
  3. renal carcinoma
  4. sepsis
  5. shock

Answer(s): A

Explanation:

The photomicrograph in figure shows recognizable glomeruli and tubules but no nuclear staining, enabling one to recognize this as a renal infarct. Most renal infarcts result from thromboemboli originating in the left ventricle of a patient who has had an MI. This woman's age and her history of an acute illness leading to her death 9 days later are compatible with this sequence of events. The histology of pyelonephritis (choice B) would show viable kidney involved in an inflammatory response. Additional findings would depend upon whether it is an acute or chronic pyelonephritis. Renal carcinoma (choice C) would show viable malignant cells and not necrotic normal renal tissue. Sepsis choice D) may show indications of the infection within the renal parenchyma with an associated inflammatory response, but this is not seen in the image. Shock (choice E) is associated with acute tubular necrosis, which is a patchy necrosis affecting the proximal more than the distal tubules, but the glomeruli remain unaffected. The image shows complete necrosis of all renal elements.



A 31-year-old previously healthy woman develops pelvic inflammatory disease and subsequently undergoes a complete hysterectomy; her ovaries are left intact. Incidental findings in the myometrium are three discrete, sharply circumscribed masses that range from 4 to 8 cm in diameter and have a whitish, whorled cut surface. What would have been the most likely outcome over the next 5 years if these masses had not been removed?

  1. complete regression
  2. continued expansile growth
  3. infiltration into surrounding tissues
  4. metastasis via blood vessels
  5. necrosis and hemorrhage

Answer(s): B

Explanation:

This description of the myometrial masses is consistent with leiomyomas, benign tumors of smooth muscle origin. Uterine leiomyomas are the most frequent tumor in women and are estimated to occur in up to 75% of women of reproductive age. As benign tumors, the expected outcome for such masses in a premenopausal woman would be continued expansile growth. Growth of leiomyomas is stimulated (but not initiated by) estrogen, therefore, regression (choice A) would be more probable in a woman of postmenopausal age or a younger woman who may have had her ovaries removed but is unlikely to be complete. Infiltration into surrounding tissues (choice C) and metastasis via blood vessels (choice D) are characteristics of malignant tumors only. While necrosis and hemorrhage (choice E) may rarely occur in benign neoplasms, they are quite characteristic of malignant neoplasms, as blood vessels are more numerous and are often poorly formed. Uterine leiomyomas and colonic adenomas are two of the exceptions to the general rule that benign neoplasms develop as single lesions.



A 47-year-old man has undergone a gradual personality change over the past 67 months with increasing moodiness and irritability During your examination you note some choreiform involuntary movements and also recognize some cognitive impairment. Afterward you talk to the man's brother who accompanied the patient to your office and he tells you that their father had similar problems for about a year prior to his death. If you could examine this patient's brain, which of the following would you expect to find?

  1. areas of demyelination of the white matter
  2. atrophy and loss of neurons of the caudate nucleus
  3. loss of pigmented neurons of the substantia nigra
  4. neurons ballooned with cytoplasmic vacuoles
  5. selective atrophy of anterior frontal and temporal lobes

Answer(s): B

Explanation:

In Huntington's disease there is a symmetric atrophy of the caudate nuclei with a great reduction in the number of neurons. The putamen is also affected but usually less so. Areas of demyelination of white matter (choice A) are the classic finding in multiple sclerosis. Loss of pigmented neurons of the substantia nigra (choice C) is a consistent change seen in Parkinson's disease. Neurons ballooned with cytoplasmic vacuoles (choice D) may be seen in a number of lysosomal storage diseases of which Tay- Sachs disease is the classic example. Selective atrophy of anterior, frontal, and temporal lobes (choice E) is seen in Pick disease. There is a severe atrophy of the frontal and temporal lobes which can be sufficient to produce the "knife-edge" appearance characteristic of this disease.