Nerve conduction studies in patients with dermatomyositis or polymyositis

Involvement of peripheral nerves in dermatomyositis (DM) and polymyositis (PM) is less well known. In the present study we retrospectively analyzed the clinical and electrophysiological records of hospital inpatients with a diagnosis of DM or PM to investigate the association of DM/PM and peripheral neuropathy.

The data of inpatients diagnosed with DM or PM were collected in Peking Union Medical College Hospital, and 186 patients (118 patients with DM and 68 with PM) were retrospectively analyzed. Nerve conduction studies (NCSs) of the median nerve, ulnar nerve, posterior tibial nerve, and common peroneal nerve were examined simultaneously.

There were 71 (38.2%) patients with abnormal NCS findings, 37 (19.9%) with pure motor involvement (decreased compound muscle action potential, CMAP), and 34 (18.3%) with peripheral neuropathy. Of the 34 peripheral neuropathy patients, 14 (7.5%) had polyneuropathy, 1 (0.5%) had multiple mononeuropathy, 16 (8.6%) had carpal tunnel syndrome (CTS), 1 (0.5%) had trigeminal sensory neuropathy, 1 (0.5%) had ulnar sensory neuropathy, and 1 (0.5%) had brachial plexus involvement. The prevalence of malignant disease (3/34, 8.8%), other connective tissue diseases (CTDs) (7/34, 20.6%) and diabetes (6/34, 17.6%) was significantly greater in DM/PM patients with peripheral neuropathy (chi(2) = 15.855, P = 0.000) compared with DM/PM patients without involvement of peripheral nerves (5/115, 4.3% and 7/115, 6.1%, respectively).

Peripheral neuropathy in DM/PM often suggests a complication with cancer, other CTDs, diabetes or CTS. From a practical point of view, NCS for DM/PM may help find the underlying disorders.