Question

Wasting of the thenar eminence and positive tinel's sign are produced due to compression of :

• A. \( \text{Common peroneal nerve} \)
• B. \( \text{Ulnar nerve} \)
• C. \( \text{Median nerve} \)
• D. \( \text{Lateral cutaneous nerve of thigh} \)

Hint:

\textbf{Neurology: Carpal Tunnel Syndrome.} Remember the key clinical features of carpal tunnel syndrome: thenar atrophy, paresthesias in the median nerve distribution, and positive Tinel's and Phalen's signs. These arise from compression of the median nerve at the wrist.

Answer 1

The Correct Option is C

Wasting (atrophy) of the thenar eminence, the group of muscles at the base of the thumb, and a positive Tinel's sign at the wrist are classic findings associated with compression of the median nerve in the carpal tunnel. This condition is known as carpal tunnel syndrome. Let's break down why: Thenar eminence wasting: The median nerve innervates three of the four thenar muscles (abductor pollicis brevis, flexor pollicis brevis superficial head, and opponens pollicis). Compression of the median nerve in the carpal tunnel leads to denervation and subsequent atrophy of these muscles, resulting in wasting of the thenar eminence. Positive Tinel's sign: Tinel's sign is elicited by tapping or percussing over the course of a nerve. A positive Tinel's sign occurs when this tapping produces a tingling or electric shock-like sensation distal to the site of compression. In carpal tunnel syndrome, tapping over the median nerve at the wrist can reproduce these symptoms in the fingers innervated by the median nerve (thumb, index, middle, and radial half of the ring finger). Now let's consider the other options: Common peroneal nerve: Compression of this nerve typically affects the muscles of the anterior and lateral compartments of the leg, leading to foot drop and sensory loss in the lateral leg and dorsum of the foot. It does not affect the thenar eminence. Ulnar nerve: Compression of the ulnar nerve typically affects the hypothenar eminence (muscles at the base of the little finger), the interossei muscles of the hand, and sensation in the little finger and ulnar half of the ring finger. Tinel's sign might be positive at the elbow (cubital tunnel syndrome) or wrist (Guyon's canal syndrome). Lateral cutaneous nerve of thigh: Compression of this nerve leads to meralgia paresthetica, characterized by numbness, tingling, and pain in the outer thigh. It does not affect motor function or sensation in the hand. Therefore, wasting of the thenar eminence and a positive Tinel's sign at the wrist are characteristic of median nerve compression in carpal tunnel syndrome.