How is EMG or NCS used in diagnosing CTS? Ulnar nerve entrapment at the elbow (cubital tunnel syndrome)?
CTS or compressive median neuropathy at the wrist is the most common entrapment neuropathy, affecting 1% of the population. CTS may show segmental nerve conduction slowing across the wrist. SNAP latencies of the median nerve are delayed most often, but with increasing severity, motor latencies can be affected. Denervation of the thenar muscles seen on needle EMG indicates moderate to severe CTS. Clinical correlation is recommended for mild CTS as sometimes NCS/EMG studies are normal despite classic symptoms of hand pain/numbness in a median nerve distribution.
In cubital tunnel syndrome, the ulnar nerve is compressed at the elbow resulting in motor or sensory nerve conduction slowing. Needle EMG examination may identify denervation in the ulnar-innervated muscles of the hand and forearm. The ulnar nerve can also be compressed at the wrist.