A. Motor nerve conduction study from the first dorsal interosseous muscle in a patient with mild cubital tunnel syndrome. Note the normal compound motor action potential (CMAP) amplitude levels are normal, but there is some slight slowing in the nerve conduction velocity across the elbow.
B. Motor nerve conduction study from the abductor digiti minimi muscle in a patient with severe cubital tunnel syndrome. There is muscle wasting and loss of two-point discrimination on this patient’s clinical exam. Note the drastically decreased compound motor action potential (CMAP) amplitude levels in addition to marked slowing in the nerve conduction velocity across the elbow.