NEURORADIOLOGY


Case 25 :
An elderly male presents with ataxia of 6 months duration. MRI is performed. What is the diagnosis?

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Imaging Findings

Findings reveal gross atrophy of the cerebellar hemispheres, with thinning of the middle cerebellar peduncle, and the pons.

Diagnosis

Olivopontocerebellar atrophy (OPCA)

Discussion

Olivopontocerebellar atrophy (OPCA) was first described in 1900 by Dejerine and Thomas. OPCA is a group of dominant inheritance and sporadic neurological disorders characterized by a chronic, progressive, cerebellar ataxia that begins in middle age. The cerebellum and its connections are the primary sites of the disease in chronic progressive disorders that often occur in familial or hereditary patterns. This neuropathological neuronal cell loss permits classification of OPCA as a non-Alzheimer's neurodegenerative illness.

The patient who presents with OPCA will most often be an adult or of late middle life up to the age of 60. The age of onset may be significantly earlier in familial cases, as distinct from sporadic cases. The clinical syndrome is characterized by classical cerebellar symptomology. OPCA presents with a chronic, slowly progressive ataxia that usually begins in the legs, and later also involves the trunk and upper limbs. The patient will exhibit impairment of equilibrium, illustrated by a positive Rhomberg sign, and walk with the typical cerebellar gait characterized by a wide stance and stiff-legged movements. Disorders of speech and swallowing are present in the clinical picture of OPCA. Dysphasia often develops in tandem with dysarthria. Dementia is not rare in OPCA patients, but is normally mild. OPCA patients do not normally exhibit the severe global dementia of the Alzheimer type.

Imaging Findings

MR not only demonstrates the morphological changes, but on T2WI demonstrates a hyperintense signal within these areas of degeneration. The importance of MR lies in its ability to differentiate OPCA from other multi system atrophy (MSA) where ataxia may be a common clinical presentation. In OPCA, the cells of dentate nuclei are preserved, as well their projection fibersto the red nuclei, and thalami thru the superior cerebellar peduncle. Hence, the demonstration of a normal superior cerebellar peduncle in the coronal plane excludes degenerative disorders associated with MSA such as Shy Drager syndrome, striatonigral degeneration, and some cases of Leigh's syndrome.

Dr. Deepak Patkar, MRI Centre, Nanavati Hospital, Mumbai