• antidepressant
• neuroleptic
• side effect

In this issue (pp 300–303) Boesch et al report on their experience with dystonia in multiple system atrophy (MSA).¹ They correctly point out the relative neglect of dystonia in previous clinical descriptions of patients with MSA. In 1986, Adams declared that dystonia was “not part of the clinical tableau” of striatonigral degeneration,² a quarter of a century after he described the disease. (Striatonigral degeneration corresponds to the MSA-P designation, carried by the bulk of the patients of Boesch et al, of current diagnostic classifications of MSA). Even when discussion focused on the motor problems caused by MSA, dystonia was not mentioned.³ These influential writings have led us to discount the likelihood of MSA causing a combination of dystonia and parkinsonism in favour of other diagnoses, such as Parkinson's disease or corticobasal degeneration.

Much as in Parkinson's disease, dystonia may be a direct manifestation of MSA or the result of treatment with dopaminergic agents. The highest previously recorded prevalence of dystonia in MSA was 12%.⁴ In the current report, dystonia was documented in 46% of untreated patients with MSA. Antecollis accounted for most of the dystonia encountered in these patients, with focal limb dystonias comprising the rest. Of note, disease related focal limb dystonia improved on levodopa in five of five patients. Over 80% of patients with a predominantly parkinsonian presentation (MSA-P) enjoyed a moderate to excellent response to levodopa initially, although this was unsustained in most. Almost half of those responsive to levodopa developed drug induced cranial-cervical dystonia. Their facial predilection and their dystonic character, regardless of distribution, seem to distinguish the drug induced dyskinesias of MSA from those seen in Parkinson's disease.

Boesch et al do not comment on the discrepancy between the high prevalence of dystonia in their series and the low occurrence rates in prior studies. Undoubtedly the observational meticulosity of the authors of this prospective study played a major role. It is also likely that focal dystonia is overshadowed in most patients by parkinsonism, cerebellar deficits, or corticospinal tract impairment. Nevertheless, Boesch et al have made an important contribution by determining that, if actively sought, dystonia may be one of the most common clinical features of MSA. The authors do note that some doubt was cast on the dystonic nature of antecollis in MSA in a recent report attributing the forward flexion of the neck to myopathy in extensor muscles.⁵

The report of Boesch et al helps flesh out our knowledge regarding the clinical repertoire of MSA. It also extends previous descriptions of the response of patients with MSA to levodopa. It is a welcome addition to our expanding body of knowledge on the clinical differential diagnosis of parkinsonism.