Abnormalities of motor cortical excitability are not correlated with clinical features in atypical parkinsonism

OBJECTIVE: To evaluate the specificity of motor cortical excitability chang es in parkinsonian syndromes and their relevance to the pathophysiology of cardinal parkinsonian features. METHODS: Paired transcranial magnetic stimulation (TMS) was used to assess cortico-cortical inhibition (CCI) and facilitation (CCF) in the opponens po llicis muscle of patients with atypical, non-L-dopa- (LD) responsive parkin sonism. RESULTS: Compared with age-matched normal control subjects, CCI (interstimu lus interval [ISI], 3 ms) was significantly reduced in 10 patients with pre dominantly parkinsonian multiple system atrophy (MSA-P) and in seven with v ascular parkinsonism (VP), but nor in four with predominantly cerebellar MS A. No significant change of CCF (ISI, 12 ms) was observed. No correlation w as found between the amount of CCI and clinical status as evaluated with th e Unified Parkinson's Disease Rating Scale (UPDRS). In 10 patients (5 MSA-P , 5 VP), CCI was significantly increased by LD acute administration without concurrent clinical changes. CONCLUSIONS: Abnormalities of CCI are not peculiar to idiopathic Parkinson' s disease and seem unlikely to underlie any specific parkinsonian feature, but rather possibly reflect a nonspecific imbalance of inhibitory and facil itatory motor cortical circuits.