Multiple system atrophy - Extrapiramidal subtype

Clinical History

A 67-year-old female patient diagnosed with Parkinson disease three years ago, with poor response to carbidopa/levodopa therapy.

Imaging Findings

Loss of volume of both putamen nuclei, with severe low signal intensity on SWI. FLAIR shows symmetric bilateral subtle linear hypointensity.
No evidence of loss of swallow-tail sign within the substantia nigra.

Discussion

Parkinsonism is a clinical syndrome characterised by rigidity, tremor, bradykinesia, and postural imbalance, it can be caused by idiopathic Parkinson Disease (PD) and by Parkinson-plus syndromes which include: Multiple System Atrophy (MSA), Progressive Supranuclear Palsy (PSP), Corticobasal Degeneration (CBD) and Dementia with Lewy Bodies (DLB). [1]
Radiologically, the best diagnostic clue for PD is the thinning of pars compacta of the substantia nigra (nigrosome 1), demonstrated as loss of the "swallow-tail sign", (presence of high signal intensity in the ventro-lateral part of the healthy substantia nigra, bordered by two lines of low signal intensity on SWI), with a sensitivity of 87.9% and a specificity of 83.3%. [2, 3] This diagnostic was ruled out because not only our patient had no evidence of loss of the swallow-tail sign, but also he had not responded to the carbipopa/levodopa therapy. However, severe low signal intensity on putamen nuclei on SWI was the main finding.
Multiple system atrophy is a progressive, idiopathic, neurodegenerative disorder. It has three clinical subtypes: Predominantly cerebellar (MSA-C) (sporadic olivopontocerebellar atrophy), predominantly extrapyramidal (MSA-P) (striatonigral degeneration) and autonomic (MSA-A) (Shy-Drager syndrome). [4]
The best diagnostic clue for MSA-P is putamen low signal intensity in dorsolateral putamen on SWI (compared to red nucleus signals better than globus pallidus), caused by abnormal iron deposition in the putamen; other features are atrophy and high signal intensity in lateral rim of putamen. [5, 6]
The imaging features for MSA-C are a cruciform shape of high signal intensity in pons on T2WI ("hot cross bun sign"), atrophy of pons, inferior olives, and cerebellum. [4]
The combination of the swallow-tail sign and putamen low signal intensity on SWI can increase the diagnostic value differentiating between MSA-P and IPD with a sensitivity and specificity of 97.4% and 83.3% respectively.[2]

Differential Diagnosis List

Final Diagnosis

Multiple system atrophy - Extrapyramidal subtype (striatonigral degeneration).

URL:	https://www.eurorad.org/case/15346
DOI:	10.1594/EURORAD/CASE.15346
ISSN:	1563-4086