Progressive Ataxia and Downbeat Nystagmus in an Adult

C. Magnesium depletion

Magnesium and calcium replacement therapy were started immediately. Thiamine was also administered. Clinical evolution was favorable with progressive improvement of symptoms, normalization of metabolic parameters, and radiological resolution of the MRI abnormalities.

The lack of family history and the speed of onset and advanced age suggested acquired ataxia. The recent history of arrhythmia and seizures indicated an extraneurological involvement, and the transient episodes of tetaniform rigidity suggested neuromuscular hyperexcitability. Notably, downbeat nystagmus can be caused by lesions at the craniocervical junction, diseases of the lower brainstem and cerebellum, or metabolic disturbances, including vitamin B₁, vitamin B₁₂, or magnesium deficiencies.¹ Therefore, vitamin deficiencies and ionic alterations were considered as explanations for the cerebellar dysfunction and cardiac dysfunction.² However, neuromuscular hyperexcitability with tetaniform rigidity made ionic disturbances the first diagnostic suspicion because of its association with metabolism of calcium and magnesium. The patient’s history of alcohol use could have been associated with toxic effects or vitamin deficiency–related ataxia, but alcohol intake had stopped more than 10 years earlier.