Arterial spin labeling hyperintensity at cerebellar nodulus: Possible indicator in downbeat nystagmus associated with hypomagnesemia

A 69-year-old woman with a history of systemic sclerosis was admitted to the emergency department because of vertigo and nausea. She had been prescribed proton pump inhibitors for several years. Physical examination revealed downbeat nystagmus (DBN) in all gaze directions. Laboratory examination revealed hypomagnesemia with a critically low serum magnesium level of 0.1 mg/dL. Head magnetic resonance imaging showed no abnormalities on T1-, T2-, or diffusion-weighted imaging; however, arterial spin labeling (ASL) revealed hyperintensity in the cerebellar nodulus (Figure 1A). She received magnesium supplementation and the proton pump inhibitors were discontinued. After 5 months of follow-up, the DBN disappeared. The magnesium levels normalized to 1.8 mg/dL and hyperintensity improved by ASL imaging (Figure 1B).

Downbeat nystagmus is associated with central vertigo.¹ It occurs due to impairments in the flocculus or nodulus of the cerebellum.^{2, 3} The underlying causes include congenital malformations, tumors, trauma, localized damage from encephalitis, and local functional issues, such as low magnesium levels.^{1, 4} A previous study has highlighted that in patients with paraneoplastic DBN, brain fluoro-d-glucose-positron emission tomography (FDG-PET) can identify increased metabolism in the cerebellar nodulus.⁵ However, FDG-PET is not generally indicated for the diagnosis of DBN. Our case suggests that similar findings can be easily identified using ASL imaging, which is less invasive and more straightforward. Arterial spin labeling imaging should be considered for patients with DBN, even if other radiological investigations do not reveal any abnormalities.

The authors declare no conflicts of interest.

Approval of the research protocol: N/A.

Informed consent: Informed consent was obtained from the patient.

Registry and the registration no. of the study/trial: N/A.

Animal studies: N/A.