To the Editor: Hyperosmolar hyperglycemic nonketotic syndrome (HHNS), a hyperglycemic emergency, can be associated with various neurological manifestations. We describe a patient with HHNS who presented with hemichorea-hemiballismus, a rare neurological manifestation characterized by a unique neuroimaging abnormality. Computed tomography (CT) scan of brain showed hyperdense striatum contralateral to the side of movement disorder. MRI showed a hyperintense lesion in the corresponding area in T1-weighted imaging, and hypointensity in T2-weighted imaging. Both the movement disorder and radiological lesions resolved completely after correction of hyperglycemia.

Hyperosmolar hyperglycemic nonketotic syndrome (HHNS), previously called hyperosmolar nonketotic coma (HONK), is a metabolic complication of diabetes mellitus characterized by hyperglycemia, extreme dehydration, hyperosmolar plasma, and various neurological manifestations. We describe a patient with HHNS who presented with hemichorea-hemiballismus (HC-HB) that resolved after correction of hyperglycemia. A 60-year-old woman with poorly-controlled diabetes presented with involuntary movement involving the right upper and lower extremities of 2 weeks' duration. The movement started initially in the right hand, and later progressed to involve right lower extremity. Physical examination revealed a middle-aged Indian woman, with normal higher mental functions and cranial nerves. We observed continuous, violent, large-amplitude jerking and flinging movements involving the right upper and lower extremity. The movement was present both in proximal and distal joints, and reduced significantly during sleep. On investigation, her initial blood glucose was 432 mg/dl, with a hemoglobin A1C of 11.5%. Her serum osmolality was 324 mOsmol/liter, and urine was negative for ketones. CBC, hepatic, renal, and thyroid function tests were within normal limits. A diagnosis of HHNS causing HC-HB was made.

A computed tomography (CT) scan of brain revealed hyperdense caudate nucleus and putamen on the left side. On further characterization, this appeared hyperintense on T1-weighted MRI and hypointense in T2-weighted imaging. The patient improved with insulin and intravenous and oral hydration. One week later, the movements were reduced to small-amplitude jerky movements involving mainly the right lower extremity. She was discharged after a few days. After 2 months of treatment, there was complete resolution of these movements. These hyperdense lesions resolved completely on a follow-up CT scan of brain, confirming the diagnosis. HCHB is a spectrum of involuntary, continuous nonpatterned movement involving one side of the body. Hemiballismus often evolves into hemichorea, hence the name HCHB.¹ The etiologies of HCHB include focal causes: ischemic or hemorrhagic stroke, neoplasm; or diffuse systemic processes: HHNS, systemic lupus erythematosus, Wilson's disease, thyrotoxicosis, etc.¹ HCHB occurring as a consequence of HHNS is a well-characterized clinico-radiological syndrome with benign outcome. It has a female preponderance, and tends to be more common in Asian patients.² Rarely, HCHB can be the presenting manifestation of diabetes in elderly persons.³ The characteristic radiological lesion is hyperdense striatum in CT scan, with MRI showing hyperintense striatum in T1-weighted images and hypo/iso intense lesion in T2-weighted images. The exact nature of basal ganglia lesion is unclear. Sequential CT and MR examination studies suggested petechial hemorrhages as a cause.⁴ Hyperviscosity, with cytotoxic edema, or ischemia resulting in incomplete infarction, are also considered to play a role.⁵ Biopsy of these lesions have disclosed a fragment of gliotic tissue with abundant gemistocytes (swollen astrocytes), which explains the shortening of T1 relaxation time. MR spectroscopy of biopsy specimens has shown findings suggestive of ischemic injury.⁶ Supporting this observation are PET studies that have shown decreased glucose metabolism in these areas, suggesting regional metabolic failure.⁷ Hyperintensity on T1WI after mild ischemia may involve a paramagnetic effect resulting from tissue manganese accumulation in these reactive astrocytes.⁶ In most cases, the movement disorder resolves within 24 to 48 hours of normoglycemia, but sometimes may last for months.^8,9