Complete loss of sensation in the C6 dermatome with normal upper extremity strength indicates a lesion at which location?

• A. Ventral root ganglia of C6
• B. Posterior interosseous nerve
• C. Medial antebrachial cutaneous nerve
• D. Dorsal root ganglia of C6

Answer: (D)

When a person has complete loss of sensation in a specific dermatome but maintains normal strength, the issue is a disruption of the sensory pathway at that spinal level rather than a problem with motor nerves. The dorsal root ganglion at a given cervical level houses the cell bodies of the sensory neurons that convey that dermatome’s sensation into the spinal cord. If the C6 dorsal root ganglion is damaged, sensation from the C6 area is lost while motor pathways remain intact, so strength is preserved.

In contrast, a lesion in the ventral root area would disrupt motor fibers and produce weakness rather than pure sensory loss. A lesion of the posterior interosseous nerve would mainly affect motor function in the forearm and hand, with sensory changes not matching the full C6 dermatome. A lesion of the medial antebrachial cutaneous nerve would cause sensory loss limited to the medial forearm, not the entire C6 dermatome. Therefore, the dorsal root ganglion of C6 best explains the finding.