Hyperglycemic hemichorea/hemiballismus is a recognized entity, seen most often in older patients, women more often than men, Type 2 diabetes mellitus (DM), presenting with a blood glucose > 400 mg/dl - and usually without ketosis. It has been reported more often in Asian women.

This may be the patient's first presentation with DM. The "classic" MR findings include unilateral or bilateral signal changes in the basal ganglia (putamen >> caudate) on MR and CT.

Most characteristic is T1 hyperintensity in the putamen; and, corresponding T2 hypointensity. CT scans may show hyperattenuation in the putamen.

In most patients, both the clinical and the imaging findings are reversible with control of blood sugar.

REFS for hyperintense basal ganglia - - LINK -
[PubMed]

Possible explanations for the imaging features (hyperattenuation on CT, Dark Bright T1, Dark T2) include blood-brain-barrier breakdown (BBB), deposition of calcium and mineralization, microhemorrhages, myelin destruction, and manganese associated with reactive astrogliosis. Some of these would be acute (contrast and hemorrhage), and others more likely to be subacute or chronic (mineralization and astrogliosis).

References below courtesy of
Michael H Lev, MD, FAHA
Director, Emergency Neuroradiology and Neurovascular Lab
Massachusetts General Hospital
Associate Professor of Radiology
Harvard Medical School
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Wintermark M, Fischbein NJ, Mukherjee P, Yuh EL, Dillon WP. Unilateral putaminal CT, MR, and diffusion abnormalities secondary to nonketotic hyperglycemia in the setting of acute neurologic symptoms mimicking stroke.
AJNR Am J Neuroradiol. 2004 Jun-Jul;25(6):975-6.
[PubMed]


Abstract
A 75-year-old Asian man presented with two episodes of chorea associated with nonketotic hyperglycemia. His chorea rapidly resolved after restitution of a normal serum glucose level, although an MR image obtained at the time of acute symptoms demonstrated high signal intensity on T1-weighted images, low signal intensity on T2-weighted images, and restricted diffusion, all involving the left putamen. A CT scan obtained 1 month later demonstrated faint hyperattenuation of the involved putamen. The reported pathophysiologic considerations for these imaging features are reviewed, and an original explanation is proposed.

Comments
AJNR Am J Neuroradiol. 2005 Jan;26(1):194; author reply 194-5. [PubMed]

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Lai PH, Tien RD, Chang MH, Teng MM, Yang CF, Pan HB, Chen C, Lirng JF, Kong KW. Chorea-ballismus with nonketotic hyperglycemia in primary diabetes mellitus.
AJNR Am J Neuroradiol. 1996 Jun-Jul;17(6):1057-64.

Abstract
PURPOSE: To describe the neuroimaging (Ct, MR, and single-photon emission CT [SPECT]) findings in a series of patients with chorea-ballismus associated with nonketotic hyperglycemia in primary diabetes mellitus and to correlate the imaging findings with the clinical presentation.

METHODS: The neuroimaging and clinical data from 10 patients with chorea-ballismus associated with nonketotic hyperglycemia in primary diabetes mellitus were evaluated. Family and drug histories, as well as other causes of chorea, were excluded. All 10 patients had CT, 5 also had MR imaging, and 3 had SPECT examinations. Three had follow-up CT and MR imaging studies, and MR findings were correlated with CT findings in 5 cases. Two experienced neuroradiologists, aware of the diagnosis but blinded to the clinical status of the patients, evaluated all images and reached a consensus as to the final
interpretation.

RESULTS: CT studies in 9 of 10 patients showed a hyperdense putamen and/or caudate nucleus; in 1, the CT findings were normal. T1-weighted MR images in all 5 patients who had MR imaging (including the patient with a normal CT study) showed hyperintense lesions without significant T2 signal alternation at the basal ganglia. In all 3 of the patients who had SPECT studies of the brain, the scans revealed hypoperfusion at corresponding areas. All 3 follow-up studies depicted resolution of the lesions in the abnormal basal ganglia. Increased hypointensity on T2-weighted and gradient-echo T2*-weighted images was also
observed in the sequential MR images. In all patients, the initial side of involvement correlated well with the neuroimaging findings. The chorea resolved within 2 days after treatment of the hyperglycemia in 9 patients.

CONCLUSION: In patients with chorea-ballismus associated with nonketotic hyperglycemia in primary diabetes mellitus, CT and T1-weighted MR images show unilateral or bilateral lesions of the putamen and/or caudate. SPECT scans show hypoperfusion. These findings may be related to petechial hemorrhage and/or myelin destruction. Early recognition of these imaging characteristics may facilitate diagnosis of primary diabetes mellitus with hyperglycemia and prompt appropriate therapy.

[PubMed]