Electromyography (EMG) and nerve conduction studies

Role in rheumatology

EMG and nerve conduction studies in rheumatology are used predominantly to confirm and characterise inflammatory myopathy (myopathic EMG pattern) and to diagnose entrapment neuropathies (e.g. carpal tunnel syndrome) that commonly complicate inflammatory arthritis
Complements muscle biopsy in the workup of suspected myositis, and is a standard test for suspected nerve entrapment in patients with inflammatory arthritis-related soft tissue swelling

Myopathic EMG pattern (small-amplitude, short-duration, polyphasic motor units with early/full recruitment) supports a primary muscle disease (inflammatory myopathy) as opposed to a neurogenic process
Nerve conduction studies localise entrapment neuropathies - e.g. carpal tunnel syndrome (prolonged median sensory/motor distal latency across the wrist) is common in RA given synovial swelling compressing the median nerve at the wrist, and in other inflammatory arthritides/connective tissue diseases with soft tissue swelling near nerve entrapment sites

EMG in suspected myositis supports (but does not replace) tissue diagnosis via muscle biopsy - the two are often performed together, with EMG helping to guide the biopsy site (though not from the exact site tested, to avoid needle-induced artefact at the biopsy site)
Entrapment neuropathy in a patient with known inflammatory arthritis should prompt assessment of local disease activity (active synovitis contributing to compression) alongside standard entrapment neuropathy management

Carpal tunnel release (surgical or conservative) for confirmed entrapment; treatment of the underlying inflammatory disease (which can improve entrapment symptoms if active synovitis is contributing to nerve compression)
For myopathy, EMG findings support the broader diagnostic and management pathway detailed in the polymyositis/dermatomyositis notes

Polymyositis/dermatomyositis, carpal tunnel syndrome (RA association), other entrapment neuropathies in inflammatory arthritis, peripheral neuropathy as a vasculitis manifestation

Nerve conduction studies specifically localise the entrapment site anatomically, which is essential for surgical planning if conservative management fails - a normal study does not fully exclude early/mild entrapment, and clinical correlation remains important

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