A patient with a C5-C6 disc prolapse compressing the C6 nerve root presents with paresthesia in the thumb and index finger, weakness of which muscle, and diminished which reflex?

• A Weakness of wrist extensors (ECRL, ECRB), biceps, and brachioradialis; diminished brachioradialis and biceps reflexes ✓
• B Weakness of deltoid (C5); diminished biceps reflex
• C Weakness of triceps; diminished triceps reflex
• D Weakness of intrinsic hand muscles; diminished finger flexion reflex

Explanation

C6 nerve root compression produces paresthesia and sensory loss in the thumb, index finger, and radial forearm (C6 dermatome). Myotome C6 primarily includes wrist extensors (extensor carpi radialis longus and brevis), biceps brachii, and brachioradialis; these muscles are weakened. The reflexes impaired are the brachioradialis and biceps jerks (both C5-C6 but C6 predominates for brachioradialis). C5 compression causes deltoid weakness and diminished biceps jerk; C7 causes triceps weakness and triceps jerk loss; C8 causes finger flexor weakness and T1 causes intrinsic hand muscle weakness.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.