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Step 2 Questions – Step 2 Daily
Study for the USMLE Step 2, daily.
A 6-year-old boy is brought into your clinic for evaluation of right-hand weakness. The mother is unsure of the onset of the weakness but has been noticing that her child rarely uses his right hand and that the right arm looks unusually limp. Physical exam reveals atrophy of both the thenar and hypothenar eminences, atrophy of the interosseous muscles, and sensory deficits on the medial side of the forearm and hand. Which of the following is the most likely location of the pathologic finding in this patient?
D. Supracondylar region of humerus
Thoracic outlet syndrome (TOS) is most likely to explain all the neurologic findings in this patient. TOS can be present as a congenital anomaly of the costoclavicular space (choice E) which is bordered by the clavicle, first rib, and the superior margin of the scapula.
The subclavian vessels and the lower trunk of the brachial plexus (C8, T1) pass through this space and can be compressed by anatomic anomalies such as congenital bands, supernumerary ribs, cervical ribs, or laxity of the costoclavicular joint. An additional finding may include the disappearance of the radial pulse when the patient turns his head to the opposite side.
The carpal tunnel (choice A) and the supracondylar region of the humerus (choice D) are common sites of injury to the median nerve. Median nerve damage does not explain hypothenar atrophy, interosseous atrophy, or numbness to the medial side of the forearm and hand, all of which are signs of ulnar nerve involvement. Therefore, the location of pathology is more proximal.
The medial epicondyle (choice B) is a common site of injury to the ulnar nerve, which may explain most of the neurologic findings except for thenar atrophy which suggests median nerve involvement. Therefore, the location of pathology is more proximal.
The shaft of the humerus (choice C) is a common site of injury to the radial nerve which is not implicated in this scenario.
BUN/Cr ratio > 20
Likely indicative of prerenal ARF
Thoracic outlet syndrome (TOS) can be present as a congenital anomaly of the costoclavicular space which is bordered by the clavicle, first rib, and the superior margin of the scapula. The subclavian vessels and the lower trunk of the brachial plexus (C8, T1) pass through this space and can be compressed by anatomic anomalies such as congenital bands, supernumerary ribs, cervical ribs, or laxity of the costoclavicular joint. An additional finding may include the disappearance of the radial pulse when the patient turns his head to the opposite side.
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