USMLE Step 1 Problem Set 20: Skin and Musculoskeletal System

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1 USMLE Step 1 Problem Set 20: Skin and Musculoskeletal System Question No. 1 of Which of the following epithelial cell junctions connects epithelial cells to their underlying extracellular matrix? Question #01 (A) Zona occludens (B) Zona adherens (C) Hemidesmosome (D) Macula adherens (E) Gap junction Zona occludens a tight junction made up of claudins and occludins that prevent diffusion. Zona adherens an intermediate junction made up of cadherins connecting to actin just below the zona occludens. C. Correct! A Hemidesmosome connects epithelial cells to their underlying extracellular matrix. Macula adherens a desmosome made up of cadherins connecting to intermediate filaments forming small, focal sites of attachment. Gap junction allows adjacent cells to communicate for metabolic and electric functions. Epithelial cells have various types of junctions: Zona occludens a tight junction made up of claudins and occludins that prevent diffusion. Zona adherens an intermediate junction made up of cadherins connecting to actin just below the zona occludens. Macula adherens a desmosome made up of cadherins connecting to intermediate filaments forming small, focal sites of attachment. Gap junction allows adjacent cells to communicate for metabolic and electric functions. Hemidesmosome connects cells to their underlying extracellular matrix. (C)Hemidesmosome RapidLearningCenter.com Rapid Learning Inc. All Rights Reserved

2 Question No. 2 of A 19 year old male tears his rotator cuff playing baseball. Which of the following shoulder muscles is not a component of the rotator cuff? Question #02 (A) Infraspinatous muscle (B) Deltoid muscle (C) Teres minor muscle (D) Supraspinatous muscle (E) Subscapularis muscle The infraspinatous muscle is a muscle component of the rotator cuff. B. Correct! The deltoid muscle is not a muscle component of the rotator cuff. The teres minor muscle is a muscle component of the rotator cuff. The supraspinatous muscle is a muscle component of the rotator cuff. The subscapularis muscle is a muscle component of the rotator cuff. A group of four shoulder muscles form the rotator cuff: Supraspinatous abduction Infraspinatous lateral rotation teres minor adduction and lateral rotation Subscapularis adduction and medial rotation (B)Deltoid muscle RapidLearningCenter.com Rapid Learning Inc. All Rights Reserved

3 Question No. 3 of 10 on paper as needed, (3) Pick the answer, and (4) Review the core concept tutorial as needed. 3. Which of the following diseases of bone is secondary to hyperparathyroidism which leads to brown tumors in bone? Question #03 (A) Osteoporosis type II (B) Osteopetrosis (C) Paget s disease (D) Osteitis fibrosa cystica (E) Polyostotic fibrous dysplasia Osteoporosis type II is senile osteoporosis affecting both sexes over the age of 70. Osteopetrosis is marble bone disease the result of osteoclast malfunction which leads to crowding of marrow spaces and resultant anemia and thrombocytopenia. Paget s disease is the result of an increase in both osteoblastic and osteoclastic activity causing a very rapid turnover of bone with resulting enlarged and deformed bones which are soft and subject to fracture. D. Correct! Osteitis fibrosa cystic is secondary to hyperparathyroidism and leads to brown tumors in bone. Polyostotic fibrous dysplasia refers to fibrous dysplasia involving more than one bone where bone is replaced with fibroblasts and collagen, resulting in irregular bony trabeculae and thinning of bone making the bone subject to fractures. Osteitis fibrosa cystica refers to an abnormal bone condition that results from hyperparathyroidism in which osteoclastic activity is increased causing cystic spaces in bone lined with osteoclasts and filled with fibrous stroma and possible heme products. These cystic lesions are referred to as brown tumors. Labs show elevated serum calcium and alkaline phosphatase with low levels of phosphorous. (D)Osteitis fibrosa cystica Question No. 4 of 10 RapidLearningCenter.com Rapid Learning Inc. All Rights Reserved

4 4. Which of the following primary tumors of bone are typically found in intramedullary bone? Question #04 (A) Enchondroma (B) Osteochondroma (C) Osteosarcoma (D) Ewing s sarcoma (E) Giant cell tumor A. Correct! Enchondroma is typically found in the intramedullary portion of bone. Osteochondroma is typically found in the metaphysis of bone. Osteosarcoma is typically found in the metaphysis of bone. Ewing s sarcoma is typically found in the diaphysis of bone. Giant cell tumor is typically found in the epiphysis of bone. Specific regions of the bone are typical locations for certain types of bone tumors: Epiphysis: benign giant cell tumor, aka osteoclastoma. Metaphysis: benign osteochondroma; malignant osteosarcoma. Diaphysis: benign osteoid osteoma; malignant Ewing s sarcoma. Intramedullary: benign enchondroma; malignant chondrosarcoma. (A)Enchondroma RapidLearningCenter.com Rapid Learning Inc. All Rights Reserved

5 Question No. 5 of A 74 year old woman is diagnosed with osteoarthritis. Which of the following arthritic components is not associated with osteoarthritis? Question #05 (A) Subchondral cysts (B) Pannus formation (C) Osteophytes (D) Bouchard s nodes (E) Heberden s nodes Subchondral cysts are associated with osteoarthritis. B. Correct! Pannus formation is not associated with osteoarthritis; it is associated with rheumatoid arthritis. Osteophytes are associated with osteoarthritis. Bouchard s nodes are associated with osteoarthritis. Heberden s nodes are associated with osteoarthritis. Osteoarthritis, aka degenerative arthritis, is a mechanical disorder involving the degradation of joints with destruction of articular cartilage, the formation of subchondral cysts, osteophytes, sclerosis, Bouchard s nodes at the PIP joints and Heberden s nodes at the DIP joints. Predisposition in the elderly, the obese, and those with joint abnormalities. Clinically experience pain after use of joint, relief with rest, and no systemic symptoms are associated with the condition. (B)Pannus formation RapidLearningCenter.com Rapid Learning Inc. All Rights Reserved

6 Question No. 6 of A 30 year old male presents with conjunctivitis, urethritis and arthritis. What does this triad of symptoms suggest? Question #06 (A) Systemic lupus erythematosis (B) Sarcoidosis (C) Polymyositis (D) Reiter s syndrome (E) CREST syndrome Symptoms and signs of systemic lupus erythematosis include fever, malaise, fatigue, weight loss, rash, Raynaud s phenomenon. Symptoms and signs of sarcoidosis include arthritis, restrictive lung disease, bilateral hilar lymphadenopathy, erythema nodosum, epithelial granulomas, uveoparotitis and hypercalcemia. Symptoms and signs of polymyositis are progressive, symmetric, and proximal muscle weakness. D. Correct! Reiter s syndrome is and autoimmune disorder which is the result of a remote bodily infection and is manifested by conjunctivitis, urethritis and arthritis. Symptoms and signs of CREST syndrome are calcinosis, Raynaud s phenomenon, esophageal dysmotility, sclerodactyly, and telangiectasia. Reiter s syndrome an autoimmune disorder as a response to infection in another part of the body, e.g., GI infection, chlamydia infection. The classic triad of symptoms is: 1. Conjunctivitis and anterior uveitis 2. Urethritis 3. Arthritis (D)Reiter s syndrome RapidLearningCenter.com Rapid Learning Inc. All Rights Reserved

7 Question No. 7 of Which of the following skin conditions is considered to be premalignant? Question #07 (A) Verrucae (B) Melasma (C) Actinic keratosis (D) Hairy leukoplakia (E) Acanthosis nigricans Verrucae are common warts and not considered to be premalignant. Melasma is hyperpigmentation of the face associated with pregnancy or oral contraceptive use and not considered to be premalignant. C. Correct! Actinic keratosis is considered to be premalignant for squamous cell carcinoma. Hairy leukoplakia refers to white painless plaques on the tongue that cannot be scraped off, caused by EBV and relatively specific for presence of HIV infection. It is not considered to be premalignant. Acanthosis nigricans refers to brown to black ill-defined velvety areas of hyperpigmentation usually found in skin folds, due to hyperplasia of the stratum spinosum. It is not considered to be premalignant. Actinic keratosis small, rough, erythematous or brownish papules that are precancerous; premalignant for squamous cell carcinoma and due to sun exposure. (C)Actinic keratosis RapidLearningCenter.com Rapid Learning Inc. All Rights Reserved

8 Question No. 8 of Which of the following blistering disorders of the skin is caused by an adverse drug reaction, potentially fatal and involves sloughing of the entire epidermis? Question #08 (A) Bullous pemphigoid (B) Stevens-Johnson syndrome (C) Pemphigus vulgaris (D) Toxic epidermal necrolysis (E) Erythema multiforme Bullous pemphigoid is an autoimmune disorder due to IgG against hemidesmosomes at the epidermal basement membrane resulting in bullae between the epidermis and dermis; affects skin but spares oral mucosa. Stevens-Johnson syndrome is manifested by fever, bullae, skin necrosis and sloughing with high mortality, usually due to an adverse drug reaction. If the entire epidermis sloughs, it is then referred to as toxic epidermal necrolysis. Pemphigus vulgaris is a more severe form of bullous pemphigoid that is potentially fatal which affects skin and oral mucosa. D. Correct! Toxic epidermal necrolysis is caused by an adverse drug reaction, potentially fatal and involves sloughing of the entire epidermis. Erythema multiforme is manifested by macules, papules, vesicles and target lesions associated with autoimmune disease, infection, drugs and cancer. Toxic epidermal necrolysis is similar to Stevens-Johnson syndrome but more severe with entire epidermal detachment. (D)Toxic epidermal necrolysis RapidLearningCenter.com Rapid Learning Inc. All Rights Reserved

9 Question No. 9 of Injury to which of the following lower extremity nerves causes a dropped foot with inability to evert/dorsiflex foot or extend toes? Question #09 (A) Common peroneal nerve (B) Obturator nerve (C) Femoral nerve (D) Inferior gluteal nerve (E) Superior gluteal nerve injury A. Correct! Common peroneal nerve injury from lateral leg trauma or fibial neck fracture causes dropped foot with inability to evert/dorsiflex foot or extends toes, with sensory deficit of anterolateral leg and dorsal foot. Obturator nerve injury from anterior hip dislocation causes inability to adduct thigh with sensory deficit of medial thigh. Femoral nerve injury from pelvic fracture causes inability to flex thigh/extend leg with sensory deficit of anterior thigh and medial leg. Inferior gluteal nerve injury from posterior hip dislocation causes inability to get up from seated position, climb stairs or jump. Superior gluteal nerve injury from posterior hip dislocation causes inability to abduct thigh. Injuries to the common peroneal nerve injury from lateral leg trauma or fibial neck fracture causes dropped foot with inability to evert/dorsiflex foot or extend toes, with sensory deficit of anterolateral leg and dorsal foot. (A)Common peroneal nerve RapidLearningCenter.com Rapid Learning Inc. All Rights Reserved

10 Question No. 10 of A 75 year old male is diagnosed with gout. Which of the following drugs is the best choice to treat acute gout? Question #10 (A) Allopurinol (B) Tylenol (C) Infliximab (D) Colchicine (E) Probenecid Allopurinol is used to treat chronic gout. Tylenol is used as an analgesic and antipyretic; it does not have anti-inflammatory properties. Infliximab is used in Crohn s disease, rheumatoid arthritis, and ankylosing spondylitis. D. Correct! Colchicine is used to treat acute gout. Probenecid is used to treat chronic gout. Colchicine is the best choice to treat acute gout. Its mechanism of action is to depolymerize microtubules thereby impairing leukocyte chemotaxis and granulation. Clinically, it is used to treat acute gout. (D)Colchicine RapidLearningCenter.com Rapid Learning Inc. All Rights Reserved