Impaired chemosensitivity to hypoxia is a marker of multiple system atrophy.

Sudden death is common in patients with multiple system atrophy (MSA). In its early stages, the cerebellar presentation MSA-C can be indistinguishable from idiopathic late-onset cerebellar ataxia. We studied the hypoxic ventilatory response in MSA-C and idiopathic late-onset cerebellar ataxia patients. Six patients with idiopathic late-onset cerebellar ataxia that later evolved to MSA had impaired hypoxic ventilatory response when minimal autonomic failure was still present, whereas for patients with unimpaired hypoxic ventilatory response their diagnosis remained idiopathic late-onset cerebellar ataxia. The demonstration of impaired hypoxic ventilatory response appears to be a good marker enabling earlier diagnosis of MSA in patients presenting with idiopathic late-onset cerebellar ataxia.