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THE LAMBERT-EATON MYASTHENIC SYNDROME
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1988
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LEMS is linked to small‑cell lung cancer through tumor‑derived antigens, while associations with other tumors are likely incidental and the trigger in non‑SCLC cases remains unknown. The study examined the clinical and electrophysiological characteristics of 50 consecutive LEMS patients. Among these patients, 62 % had underlying SCLC—most within two years of symptom onset—with universal proximal lower‑limb weakness, depressed reflexes, post‑tetanic potentiation, autonomic dryness, and ptosis, and nearly all displayed abnormal evoked potentials and single‑fiber EMG findings, while the risk of SCLC falls sharply after two years.
The clinical and electrophysiological features of 50 consecutive patients with the Lambert-Eaton myasthenic syndrome (LEMS) have been analysed. Carcinoma was detected (CD group) in 25, of whom 21 had small cell lung cancer (SCLC). SCLC was evident within 2 yrs of onset of LEMS symptoms in 20/21 cases, and at 3.8 yrs in 1/21. In the cases in whom no carcinoma was detected (NCD group), 14/25 had a history of LEMS > 5 yrs. The dominant neurological features were similar in the CD and NCD groups, and consisted of proximal lower limb weakness (100%), depressed tendon reflexes (92%) with posttetanic potentiation (78%), autonomic features, especially dryness of the mouth (74%) and mild/moderate ptosis (54%). The compound evoked muscle action potential amplitude in abductor digiti minimi was below the lower limit of control values in 48/50, and the increment following maximum voluntary contraction above the upper limit of control values in 48/50. Single fibre electromyographic abnormalities were found in 29/29 cases. The analysis indicates that a patient presenting with LEMS has a 62% risk of an underlying SCLC, and that this risk declines sharply after 2 yrs, becoming very low at 4 to 5 yrs. It is argued that in SCLC cases antigenic determinants on tumour cells initiate the autoimmune response, often early in the course of the malignancy, but that the association of LEMS with tumours other than SCLC may be fortuitous. In the latter, and in NCD patients, the initiating factor(s) are unknown.