Lexical processing in Parkinson's disease and multiple sclerosis.

Patients with Parkinson's disease (PD) or multiple sclerosis (MS) were categorized as normal in naming (NN) or impaired in naming (IN) based on their performance on the Boston Naming Test. All patients scored at least 23 on the Mini-Mental State Examination. Both PDIN and MSIN patient groups exhibited poor naming performance when target words were elicited with semantic, visual or rhyming cues. They also performed poorly on the vocabulary subtest of the Wechsler Adult Intelligence Scale-Revised and had difficulty repeating sentences. PDNN and MSNN patients showed more selective deficits. These findings add to a growing literature demonstrating that language in general, and naming in particular, can be compromised in subcortical diseases even when global mental status is only mildly affected. The clinical implications of these observations are, however, unclear.