Functional imaging with positron emission tomography in multiple system atrophy

Although the current guidelines for the clinical diagnosis of multiple system atrophy (MSA) do not require structural or functional brain imaging, investigations utilizing positron emission tomography (PET) have been helpful diagnostically in differentiating between MSA and primary autonomic failure; idiopathic Parkinson's disease; and sporadic olivopontocerebellar atrophy. These investigations have demonstrated different patterns of cerebral glucose utilization and of nigrostriatal projection abnormalities among these disorders and between the cerebellar and parkinsonian forms of MSA. Most of the studies have focused upon patients with well-established disease and none have examined the utility of PET imaging in early stage patients with follow-up of clinical course and autopsy verification to ensure accuracy of diagnosis and to determine the sensitivity and specificity of PET techniques for diagnosis. Recent PET studies have revealed denervation of myocardial post-ganglionic sympathetic neurons in some MSA patients, indicating that this disorder can affect the peripheral autonomic as well as the central nervous system. Investigations utilizing ligands to quantify central nervous system dopaminergic and cholinergic terminals have begun to provide insight into the neurochemical disorders that may underlie two of the sleep disturbances common in MSA, rapid eye movement sleep behavior disorder and obstructive sleep apnea.