神経伝導検査を「読む」

抄録

Nerve conduction study (NCS) is essential for the diagnosis of neuromuscular disorders. NCS is an extended physical examination, and NCS results have only limited value without clinical information. Here I describe “How to read NCS” on a case–by–case basis. 1) When revealing the cause of weakness. NCS is useful, when the origin of the muscle weakness exists in the peripheral nervous system. Abnormality of CMAP in the muscle with weakness suggests that the weakness can be of peripheral nerve origin. Normal CMAP in the muscle with apparent weakness suggests that the origin of the weakness exists in the proximal sites, including central nervous system. 2) When revealing the cause of sensory disturbance. SNAP abnormality in the site with apparent sensory loss supports the idea that the origin of sensory loss is peripheral nerve. If normal SNAP was recorded from site with sensory loss, it suggests that the cause of sensory loss exists in the proximal site of stimulation point (acute phase), or in the proximal site of spinal ganglion including central nervous system (chronic phase). 3) Assessment of unexpected results. In Lambert–Eaton myasthenic syndrome, extremely small CMAP can be recorded from the muscle with normal strength. In the inclusion body myositis, CMAPs from hand muscles are often normal even in patients with weak handgrip. The origin of muscle weakness in inclusion body myositis usually is in forearm muscles, but not in the hand muscles.