Myasthenic syndrome caused by direct effect of chloroquine on neuromuscular junction
W. Robberecht, J. Bednarik, P. Bourgeois, J. van Hees and H. Carton
Department of Neurology, University Hospital Leuven, Belgium.
Chloroquine induced a myasthenic syndrome in a patient taking the drug for
presumable reticular erythematous mucinosis. Clinical features and results
of single-fiber electromyography were typical for a failure of
neuromuscular transmission, while peripheral nerves and muscles were intact
on clinical, biochemical, electrophysiologic, and pathologic investigation.
The time course of the clinical and electrophysiologic findings during
provocation with chloroquine and the absence of autoantibodies indicate
that the syndrome was due to a direct effect of the drug on the
neuromuscular junction. While not taking chloroquine, the patient showed a
decremental response on a modified double-step nerve stimulation test and a
mean consecutive difference on single-fiber electromyography that was at
the upper limit of normal, indicating a subclinical impairment of
neuromuscular transmission. These findings can explain the apparent rarity
of the syndrome described, as a direct effect of chloroquine on the
neuromuscular junction may only have clinical relevance in patients with a
reduced neuromuscular safety factor.
