What is the role of EMG and nerve conduction studies in the workup of CNS lupus?

Updated: May 04, 2021
  • Author: Pradeep C Bollu, MD; Chief Editor: Niranjan N Singh, MBBS, MD, DM, FAHS, FAANEM  more...
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Electromyography (EMG) and nerve conduction studies provide useful data in the clinical assessment of peripheral complications of systemic lupus erythematosus (SLE).

Muscle weakness in patients with SLE may result from inflammatory myopathy, medication-induced myopathy, neuromuscular junction dysfunction, neuropathies, or from other musculoskeletal disturbances. Although much of the clinical decision-making relies on examination and historical evidence (especially time course of drug therapy with steroids or hydroxychloroquine), EMG may be useful in distinguishing inflammatory from noninflammatory myopathy.

Lupus myositis resembles dermatomyositis or polymyositis on EMG findings, including increased insertional activity, fibrillations and positive sharp waves, and myopathic motor unit potentials and recruitment patterns, as well as complex repetitive discharges. Lupus myositis may present with normal EMG findings, especially (but not exclusively) if partially treated, so that a normal needle examination does not exclude inflammatory myositis in SLE.

Repetitive stimulation studies may be used to search for neuromuscular junction pathology analogous to that seen with either myasthenia or myasthenic syndrome. (This is rare in SLE but has been reported.)

Peripheral nerve dysfunction in SLE presents clinically as mononeuritis multiplex, symmetrical distal polyneuropathy (sensory or sensorimotor), or acute demyelinating polyradiculopathy. The typical findings of each of these conditions may be demonstrated on conventional nerve conduction studies. As with other causes of acute polyradiculopathy, proximal nerve conduction studies or F and H wave studies may be needed to demonstrate proximal dysfunction, especially early in the course of the disease.

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