Lambert-Eaton myasthenic syndrome
Lambert-Eaton myasthenic syndrome (LEMS) is usually paraneoplastic (P-LEMS) and classically presents as a generalised muscle weakness with diplopia, ptosis, and hyporeflexia. It is due to autoantibodies directed against the presynaptic P/Q-type voltage-gated calcium channels (VGCC), and there is good evidence that different antibodies tend to be involved in the non neoplastic (NP-LEMS) and the paraneoplastic variants . In small cell carcinoma often this is due to anti-glial nuclear antibody against SOX-1. It has also been reported after varenicline and botulinum toxin use.
- Proximal muscle weakness
- Legs more than arms
- Augmentation of strength during initial voluntary activation
- Depressed deep tendon reflexes
- Post-tetanic potentiation
- Autonomic dysfunction
- Dry mouth
- Erectile failure
- Rarely bulbar or respiratory involvement
- In 60% underlying malignancy
- P-LEMS in particular can be associated with cerebellar degeneration
- EMG - small compound muscle action potentials and facilitation with exercise or 20-Hz repetitive stimulation is characteristic compared to the picture in myasthenia gravis.
- Remove underlying cause - multiple cures with treatment or resection of initiating malignancy or potentiating drug
- aminopyridines - 3,4-diaminopyridine may be more effective than pyridostigmine, but patients may prefer the later as fewer side effects.
- ↑ Pellkofer HL, Armbruster L, Krumbholz M, Titulaer MJ, Verschuuren JJ, Schumm F, Voltz R. Lambert-eaton myasthenic syndrome differential reactivity of tumor versus non-tumor patients to subunits of the voltage-gated calcium channel. Journal of neuroimmunology. 2008 Nov 15; 204(1-2):136-9.(Link to article – subscription may be required.)
- ↑ Sabater L, Titulaer M, Saiz A, Verschuuren J, Güre AO, Graus F. SOX1 antibodies are markers of paraneoplastic Lambert-Eaton myasthenic syndrome. Neurology. 2008 Mar 18; 70(12):924-8.(Link to article – subscription may be required.)
- ↑ a b Maddison P, Newsom-Davis J. Treatment for Lambert-Eaton myasthenic syndrome. Cochrane database of systematic reviews (Online). 2005; (2):CD003279.(Epub) (Link to article – subscription may be required.)
- ↑ Wirtz PW, Verschuuren JJ, van Dijk JG, de Kam ML, Schoemaker RC, van Hasselt JG, Titulaer MJ, Tjaden UR, den Hartigh J, van Gerven JM. Efficacy of 3,4-diaminopyridine and pyridostigmine in the treatment of Lambert-Eaton myasthenic syndrome: a randomized, double-blind, placebo-controlled, crossover study. Clinical pharmacology and therapeutics. 2009 Jul; 86(1):44-8.(Link to article – subscription may be required.)