Hyperosmotic hyperglycaemic nonketotic syndrome (HHNS) induced hemichorea and hemiballismus: A case report

Clinical History

A 60-year-old female patient presented in peak summer conditions with involuntary movements of the right wrist for the past ten days, which aggravated progressing to involve the entire right upper limb for three days. The patient was referred to the radiology department for MRI evaluation of the brain.

Imaging Findings

On the T2 W axial images, there is evidence of hypointensity across the left-sided caudate head and putamen. The right-sided caudate head and putamen appear normal. On the T2 TIRM axial sections left caudate head and putamen appear hypointense. On the T1 W axial images, there is evidence of hyperintensity across the left-sided caudate head and the putamen. No obvious diffusion restriction is seen on the diffusion weighted sequence. On correlative CT axial images, there is evidence of hyperdensity seen across the left-sided caudate head and the putaminal region.

Discussion

Hyperosmotic hyperglycaemic nonketotic syndrome (HHNS) is a metabolic complication of diabetes mellitus. The syndrome is characterized by hyperglycaemia, extreme dehydration, hyperosmolar plasma and neurological manifestations. This syndrome was previously called hyperosmolar nonketotic coma (HONK) [1]. Nonketotic hyperglycaemia is usually observed in patients with type 2 Diabetes mellitus [2]. It has a female preponderance and tends to be more common in Asian patients [1]. Nonketotic hyperglycaemic patients present with neurological abnormalities including hemichorea, seizure, hemianopsia and coma [2]. HemiChoreaHemiBallismus (HCHB) is a spectrum of involuntary, continuous non-patterned movements involving one side of the body. Hemiballism-hemichorea caused by nonketotic hyperglycaemia was first reported by Bedwell in 1960 [2].
The pathophysiologic mechanisms underlying the imaging findings are unclear. Sequential CT and MR examination studies suggest petechial haemorrhages as a cause. Hyperviscosity with cytotoxic oedema, or ischaemia resulting in incomplete infarction, are also considered to play a role. Biopsy of these lesions reveals a fragment of gliotic tissue with abundant swollen astrocytes, which explains hyperintensity on T1WI. MR spectroscopy of biopsy specimens show findings of ischaemic injury. PET studies show decreased glucose metabolism in these areas, suggesting regional metabolic failure. Hyperintensity on T1WI after mild ischaemia may involve a paramagnetic effect resulting from tissue manganese accumulation in these reactive astrocytes [4]. Imaging findings include CT and MRI evaluation. Computed tomography of the brain reveals hyperdense caudate nucleus and putamen on the contralateral side [1]. The T1-weighted MR images showed unilateral hyperintensity in the putamen and caudate. The findings on the T2-weighted MR images varied. Gradient echo images and DWI showed no susceptibility artefact [4]. Striatal and cerebellar involvement has also been reported [1, 3]. In most cases, the movement disorder resolves within 24 to 48 hours of normoglycaemia [1]. Recognition of the association of these neurological and radiological abnormalities with nonketotic hyperglycaemia is important because correction of the underlying hyperglycaemia will lead to rapid improvement [2].
In this case MRI evaluation of the brain for clinical symptoms of hemiballismus was performed, provisional diagnosis of HHNS was made and the patient was tested for random blood sugar level which was 448 mg/dl. As a result the patient’s uncontrolled diabetic status was revealed and our diagnosis of HHNS was confirmed. The patient was treated with oral rehydration and insulin, and recovered within 48 hours. Once diabetic treatment was started and sugar levels were maintained, the patient did not have any relapse. So we finally came to the understanding that in this diabetic patient dehydration resulted in hyperosmolar status leading to hyperosmotic hyperglycaemic nonketotic syndrome (HHNS).

Differential Diagnosis List

Final Diagnosis

Hyperosmotic hyperglycaemic nonketotic syndrome (HHNS) induced hemichorea and hemiballismus

URL:	https://www.eurorad.org/case/12055
DOI:	10.1594/EURORAD/CASE.12055
ISSN:	1563-4086