A 65-year-old man is evaluated for slowly progressive, right-hand clumsiness for several months. Medical history is significant for hypertension and end-stage renal disease, for which he undergoes hemodialysis 3 times a week. The patient is retired and not physically active. He does not use tobacco, alcohol, or illicit drugs. Blood pressure is 130/90 mm Hg and pulse is 80/min. BMI is 20 kg/m². Examination shows decreased sensation over the 4th and 5th fingers of the right hand, along with a weaker grip and weaker hand flexion at the wrist compared to the left side. Overall muscle mass and tone are decreased in all four extremities. Which of the following is the most likely site of nerve injury?

Question

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Explanation: The ulnar nerve passes behind the medial epicondyle at the elbow and into the forearm, where it innervates the flexor carpi ulnaris and medial portion of the flexor digitorum profundus. It then passes through the wrist and into the hand, where it provides sensory innervation to the medial aspect of the hand and the medial 1 ½ digits and motor innervation to multiple intrinsic hand muscles (eg, hypothenar muscles, medial lumbrical muscles, adductor pollicis). ulnar nerve Injury to the ulnar nerve at the wrist (eg, hamate fracture, compression from a bicycle handlebar) can cause numbness and paresthesia at the medial side of the hand along with intrinsic hand weakness that patients may describe as "clumsiness." Injury at the elbow will cause similar symptoms along with decreased grip strength (due to denervation of the flexor muscles in the forearm) and weaker hand flexion at the wrist (flexor carpi ulnaris). This patient has sensory features in an ulnar nerve distribution; his decreased grip strength and weaker wrist dorsiflexion confirm the location of injury at the elbow rather than the wrist (Choice F). The ulnar nerve can be compressed by prolonged leaning on the elbow or sleeping with the elbow in extreme flexion. It can also be injured by a direct blow (ie, "hitting the funny bone"). Patients with end-stage renal disease can develop ulnar neuropathy due to positioning during hemodialysis; chronic uremia causes further vulnerability due to generalized muscle wasting and loss of subcutaneous soft tissue. (Choices A and B) Compression of the median nerve at the wrist (ie, carpal tunnel syndrome) causes sensory symptoms in the lateral fingers; compression at the elbow causes additional sensory findings over the thenar eminence. Although some patients have symptoms in the lateral aspect of the 4th finger, involvement of the 5th is inconsistent with a median nerve injury. median nerve lateral fingers (Choices C and D) Supracondylar humerus fractures can injure the radial nerve at the elbow. This causes weakness of hand/finger extensor muscles and sensory loss over the posterior forearm/dorsolateral hand. Distal radial neuropathy can be caused by external compression or repeated pronation and supination of the wrist; sensory findings involve the lateral (not medial) hand, and motor deficits are typically minor. Supracondylar humerus fractures forearm/dorsolateral hand Educational objective: The ulnar nerve is vulnerable to injury where it runs posterior to the medial epicondyle at the elbow. Features include decreased sensation in the medial hand, decreased grip strength, and weakness of intrinsic hand muscles.

A 65-Year-Old Man Is Evaluated for Slowly Progressive, Right-Hand Clumsiness