Diagnosing Multiple System Atrophy-Use of Paraclinical Measures
ABSTRACTS & COMMENTARY
Sources: Schrag A, et al. Clinical usefulness of magnetic resonance imaging in multiple system atrophy. J Neurol Neurosurg Psychiatry 1998;65:65-71; Delalande I, et al. Do visual-evoked potentials and spatiotemporal contrast sensitivity help to distinguish idiopathic Parkinson's disease and multiple system atrophy? Mov Dis 1998;13:446-452.
In a study by schrag and associates, the brain MRIs of 44 patients with multiple system atrophy (MSA), 47 patients with idiopathic Parkinson's disease (PD), and 45 age-matched controls were reviewed in a blinded fashion. Of high specificity (> 90%) but lower sensitivity (73-88%) for MSA, Schrag et al found putaminal atrophy, a hyperintense putaminal rim, and infratentorial signal change. Finding any infratentorial change gave a higher sensitivity but a lower specificity.
Delalande and colleagues studied 12 patients with PD and 12 patients with MSA, as clinically determined by the presence of parkinsonism with the addition of two or more signs: autonomic failure, clinical signs of cerebellar or pyramidal tract involvement, or cerebellar or brainstem atrophy on neuroimaging.
Delalande et al found significant delays in the latency of the P100 and N3 of PD patients, while such delays in the visual-evoked potential (VEP) was not present in MSA. There was also an intraocular difference in static visual contrast sensitivity of PD patients, not evident in MSA.
COMMENTARY
The diagnosis of MSA in life and differentiation from PD is difficult, particularly in the early stages of disease. MSA patients have parkinsonian features that are not DOPA-responsive along with autonomic failure and signs of cerebellar degeneration. At autopsy in MSA, there is loss of neurons and gliosis in the substantia nigra and preganglionic nuclei of the medulla and spinal cord. Unlike PD, there is no Lewy body formation.
The studies by Schrag et al and Delalande et al demonstrate the use of a few simple paraclinical measures, MRI scanning, and VEPs, in assisting in an accurate diagnosis of MSA or PD. Thus, the presence of putaminal atrophy with signal changes in the putamen and infratentorial structures had a reasonable positive predictive value of 85-93% for MSA. It has been known for years that PD patients have abnormal VEPs, presumably from a dopaminergic deficiency in the visual pathways starting at the level of the retina. Such delays in VEPs were not found by Delalande et al in the MSA, offering another objective marker to distinguish the two disorders.
Of course, both studies are limited because the clinical diagnoses do not have an autopsy confirmation. Nonetheless, the ability to make an earlier and more accurate diagnosis of MSA may permit the testing of novel drug therapies. Saper provides a recent helpful review of the overlapping, yet distinct neuropathology of these two disorders.1 -ba
Reference
1. Saper CB. "All fall down:" The mechanism of orthostatic hypotension in multiple systems atrophy and Parkinson's disease. Ann Neurol 1998;43:149-151.
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