Unilateral drop finger due to cervical spondylosis at the C6/7 intervertebral level.

A 64-year-old man who presented right drop fingers without pyramidal signs due to cervical spondylosis is reported. Magnetic resonance imaging showed a high signal intensity change on T2-weighted scans of the spinal cord at the C6/7 intervertebral level. Evoked spinal cord potentials following ulnar nerve stimulation were attenuated at the C6/7 intervertebral level. Compound muscle action potentials (CMAPs) following right cervical nerve root stimulation were recorded from the extensor digitorum communis. CMAPs following right C8 nerve root stimulation were evoked with small amplitudes. Small polyphasic CMAPs with prolonged onset latency were recorded following right C7 nerve root stimulation. Simultaneous C7 radiculopathy and C8 segmental spinal cord lesion due to cervical spondylosis at the C6/7 intervertebral level were the causes of drop fingers in the present case. Unilateral drop finger is a clinical symptom commonly associated with posterior interosseus nerve palsy, but mention should be made about cervical lesions causing drop finger. Electromyographic abnormalities of the triceps and first dorsal interosseus muscle were the key findings for differentiating the cause from paralysis of the posterior interosseous nerve.