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Autonomic dysfunction in the Lambert-Eaton myasthenic syndrome

Serologic and clinical correlates

From the Departments of Neurology (Drs. O'Suilleabhain, Low, and Lennon), Immunology (Dr. Lennon), and Laboratory Medicine and Pathology (Dr. Lennon), Mayo Clinic, Rochester, MN.

Address correspondence and reprint requests to Dr. Vanda A. Lennon, Neuroimmunology Laboratory, 828 Guggenheim Building, Mayo Clinic, 200 First Street SW, Rochester, MN 55905.

Autonomic dysfunction is a recognized feature of the Lambert-Eaton myasthenic syndrome (LES). However, the characteristic pattern of dysautonomia has not been clearly documented and its pathophysiologic basis is not known. We therefore abstracted autonomic symptomatology and results of quantitative tests for salivation, and vasomotor, cardiovagal, and sudomotor reflexes from records of 30 LES patients. Dry mouth (77%) and impotence (45% of men) were the most common symptoms. Composite Autonomic Scoring Scale results were abnormal in 93% of patients, and autonomic failure was severe in 20%. The frequency of specific test abnormalities were the following: sudomotor function, 83%; cardiovagal reflexes, 75%; salivation, 44%; and adrenergic function, 37%. Although voltage-gated N-type calcium (Ca²⁺) channels are implicated in autonomic transmission, the low frequency of serum antibodies to N-type Ca²⁺ channels found in the patients of this study(31% positive) argues against a pathogenic role in mediating LES-related dysautonomia. In contrast, 93% of the patients were seropositive for P/Q-type Ca²⁺ channel antibodies. A subset of these antibodies is thought to impair neuromuscular transmission. Autoantibodies of thyrogastric or glutamic acid decarboxylase specificity (markers of predisposition to type 1 diabetes mellitus) were found in 45% of patients, and type 1 antineuronal nuclear antibody (or anti-Hu, a marker of autoimmune neuropathy associated with small-cell lung carcinoma) was found in 3%. No autoantibody correlated with autonomic dysfunction severity. Sensorimotor neuropathy was documented in five patients, and was not significantly associated with autonomic neuropathy. Autonomic failure was most severe in older subjects with cancer (p = 0.02, age by cancer interaction).

Supported in part by NCI grant CA-37343 (V.A.L.) and PO1-NS-32352(P.A.L.).

Received December 30, 1996. Accepted in final form July 17, 1997.

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