EMG and Nerve Conduction Studies Explained: Neuropathy, Radiculopathy and Motor Neurone Disease

NCS and EMG are the reference bedside neurophysiology tests for peripheral neuromuscular symptoms. NCS: stimulates sensory or motor nerves and records amplitude, latency, and conduction velocity. Axonal neuropathy = low amplitude, relatively preserved conduction velocity. Demyelinating neuropathy (GBS, CIDP, hereditary demyelinating) = slowed conduction, prolonged distal latency, temporal dispersion, conduction block. EMG: needle electrode in muscle assesses spontaneous activity (fibrillations, positive sharp waves — signs of denervation) and motor unit potentials during volitional activation. Findings help localise: motor neurone disease shows widespread active denervation + reinnervation; radiculopathy shows changes limited to a myotome; carpal tunnel shows median sensory latency prolongation across the wrist. Common indications: suspected carpal tunnel, cubital tunnel, radiculopathy failing conservative management, diabetic neuropathy assessment, GBS/CIDP diagnosis, myopathy (with muscle biopsy), and motor neurone disease. Not necessary in classic clinical carpal tunnel with clear median distribution — treat empirically. Special: single-fibre EMG is the reference for myasthenia gravis; repetitive nerve stimulation confirms neuromuscular junction disorders.