Multiple sclerosis masquerading as lithium toxicity.

The author presents a case report of a manic-depressive patient who developed dysarthria and ataxia while on lithium maintenance. These symptoms were erroneously attributed to lithium toxicity occurring at therapeutic serum levels. However, the symptoms persisted despite diminution in lithium dosage and a neurological consultation revealed the diagnosis of multiple sclerosis. The author concludes that lithium therapy is effective with manic-depressive patients, that adverse side effects are infrequent and can occur at toxic or therapeutic serum lithium levels, and that the exceptional patient may have a second illness incorrectly attributed to lithium toxicity.