Assessment of Ulnar Neuropathy
The most likely site of ulnar nerve damage is in the region of the shallow ulnar groove at the elbow where the nerve is prone to stretching or injury.
Nerve conduction studies check:
• the preservation of the ulnar sensory responses from the little finger
• any evidence of slowing of the speed of nerve impulses across the site of pressure at the elbow compared to the forearm
• any drop in the size of the muscle response when a stimulus is given above, compared to below, the elbow. This would be consistent with a block in the number of nerve impulses getting through the site of entrapment.
Less common causes of an ulnar nerve lesion include a deep ulnar nerve lesion at the level of the wrist
This can occur with pressure on the ulnar nerve at the wrist e.g. albeit uncommonly with cycling
Use of MRI or ultrasound as ancillary measures to nerve conduction studies
Nerve conduction studies remain the diagnostic mainstay, but when electrodiagnostic findings are not localising, ultrasonography or MR imaging of the elbow may support a diagnosis of ulnar neuropathy at that level.MR imaging of the elbow may show increased signal within the ulnar nerve, both above and below the site of entrapment, sometimes with swelling of the nerve, confirming evidence of an ulnar neuropathy (Britz G et al., 1996).
Britz G et al., Ulnar nerve entrapment at the elbow: correlation of magnetic resonance imaging, clinical, electrodiagnostic and intra-operative findings. Neurosurgery 1996, March, Vol 38, No. 3