Immune-mediated spastic ataxia masquerading as clinically probable multisystem atrophy in an elderly woman

Background

Autoimmune neurological syndromes pose diagnostic challenges due to their resemblance to neurodegenerative conditions. Autoimmune spastic ataxia is a rare phenomenon. This case presents a 56-y-old woman with subacute-onset spastic ataxia, highlighting the complexities in diagnosis and the role of autoimmunity in such cases.

Case Presentation

A woman in her fifties developed progressive spastic ataxia over a year and presented to our outpatient department for evaluation. The patient exhibited clinical signs including saccadic intrusions, gaze-evoked nystagmus, mixed dysarthria, spasticity, exaggerated reflexes, and cerebellar dysfunction. Brain magnetic resonance imaging (MRI) displayed the “hot cross bun sign” and cerebral and cerebellar atrophy. Initial tests yielded minimal abnormalities, but a positive antinuclear antibody (ANA) emerged. The patient initially declined immunotherapy. Upon symptom progression, a repeat cerebrospinal fluid (CSF) analysis showed inflammatory changes and a whole-body positron emission tomography (PET) scan indicated reduced uptake in the cerebellum and brainstem. Subsequent paraneoplastic antibody testing revealed an unspecified neuronal antibody targeting capillaries and arterioles. Treatment with steroids, plasmapheresis, and azathioprine led to sustained improvement, reducing spasticity, and enabling her to walk short distances.

Conclusions

This case emphasizes the diagnostic complexity of autoimmune neurological syndromes, particularly spastic ataxia. Autoimmune etiology should be considered even when neurodegenerative conditions seem likely. The presence of neuronal antibodies, inflammatory CSF, and response to immunotherapy underscores the role of autoimmunity in this case. Additionally, the “hot cross bun sign” may not always signify neurodegeneration, but can indicate immune-mediated neural damage. Recognizing autoimmune involvement early offers therapeutic possibilities and highlights the need for a comprehensive diagnostic approach in such cases.