Electrodiagnostic Study of Phrenic Nerve Function in Patients with Systemic Lupus Erythematosus

Background: Systemic lupus erythematosus (SLE) may affect respiratory muscles. Diaphragmatic weakness in patients with SLE is a controversial issue and is claimed to have a neuropathic, myopathic or unknown pathogenesis. Objectives: To determine whether the diaphragmatic weakness could be explained on the basis of a phrenic neuropathy in patients with SLE. Methods: A total of 21 patients (18 female 3 male) with systemic lupus erythematosus (SLE) (age range, 16-36yr) were included and studied by physical chest examination, chest radiography, spirometry, as well as serological examinations and bilateral transcutaneous phrenic nerve conduction studies. Results: 14 (66.6%) patients complained of dyspnea, only one patient showed paradoxical abdominal movement. Pulmonary function tests showed proportional reduction of the forced vital capacity (FVC) and forced expiratory volume in 1 second (FEVj) in 17 (81%) patients, suggesting a restrictive process which was severe in 5 (23%) patients. Phrenic nerve evaluation using transcutaneous stimulation studies showed delayed latencies of the right, left both phrenic nerve in 17 (81%), 19 (90%) and 17 (81%) patients respectively, confirming a demyelinating neuropathy. Also Phrenic nerve stimulation evoked a low-amplitude response from right, left and both phrenic nerve in 17 (81%), 15 (71%) and 14 (66.6%) of patients respectively, confirming axonal neuropathy. There were no significant differences in serum immune markers between individuals with and those without abnormal electrical phrenic nerve stimulation. All patients presented with dyspnea showed abnormal phrenic nerve conduction studies. There was tendency for small but clear lung fields in CXR of individuals with abnormal electrical phrenic nerve stimulation. Overall FVC % predicted was decreased in individuals with abnormal electrical phrenic nerve stimulation compared to those without. Conclusions: Diaphragmatic weakness in patients with SLE is both common and is very likely to be caused by a phrenic neuropathy with evidence of bilateral involvement in patients with SLE.