A 40-year-old tailor complains of pain, numbness, and weakness of the right hand for the last three months. On examination, there is hypoaesthesia and atrophy of thenar eminence. Which one of the following nerves is likely to be involved?
## **Core Concept**
The question tests knowledge of peripheral nerve anatomy and its correlation with clinical symptoms. The symptoms described, such as pain, numbness, weakness, hypoaesthesia, and atrophy of the thenar eminence, point towards a neuropathy affecting the nerves supplying the hand. The thenar eminence is primarily innervated by the median nerve.
## **Why the Correct Answer is Right**
The median nerve is responsible for innervating the thenar eminence muscles (thumb muscles) and provides sensation to the palmar surface of the thumb, index, middle finger, and the radial half of the ring finger. The symptoms described, particularly the atrophy of the thenar eminence and hypoaesthesia, are classic for median nerve involvement. This condition is commonly known as carpal tunnel syndrome (CTS), which is often seen in individuals performing repetitive tasks with their hands, such as typing or, in this case, possibly sewing.
## **Why Each Wrong Option is Incorrect**
- **Option A:** The ulnar nerve primarily supplies the intrinsic muscles of the hand (except those of the thenar eminence and lateral two lumbricals), and sensory innervation to the little finger and the ulnar half of the ring finger. While ulnar nerve damage can cause hand weakness and numbness, it does not typically cause thenar eminence atrophy.
- **Option B:** The radial nerve supplies the muscles of the posterior arm and forearm (extensors), and sensation to the back of the arm, forearm, and hand. Damage to the radial nerve would more likely cause wrist drop and sensory loss on the back of the hand rather than thenar atrophy.
- **Option D:** The musculocutaneous nerve supplies the biceps brachii, brachialis, and coracobrachialis, and its injury would primarily affect elbow flexion and forearm supination, not hand function or thenar eminence.
## **Clinical Pearl / High-Yield Fact**
A key clinical test for diagnosing median nerve compression (as in carpal tunnel syndrome) is the Tinel's sign, where tapping over the median nerve at the wrist elicits tingling sensations in the distribution of the median nerve. Another important fact is that the thenar eminence is primarily innervated by the **median nerve**, making its atrophy highly suggestive of median nerve pathology.
## **Correct Answer:** . Median nerve.