Neurology India Medknow Publications on behalf of the Neurological Society of India ISSN: 0028-3886 EISSN: 1998-4022 Vol. 59, Num. 2, 2011, pp. 293-294

Neurology India, Vol. 59, No. 2, March-April, 2011, pp. 293-294

Letter to Editor

"Hot cross bun" sign in HIV-related progressive multifocal leukoencephalopathy

Ravi Yadav¹, Mahendra Ramdas¹, N Karthik¹, Girish Baburao Kulkarni¹, Rose Dawn², M Veerendra Kumar¹, D Nagaraja¹

¹ Department of Neurology, National Institute of Mental Health and Neurosciences (NIMHANS), Bangalore, India
² Department of Neuroradiology, National Institute of Mental Health and Neurosciences (NIMHANS), Bangalore, India

Correspondence Address: Ravi Yadav, Department of Neurology, National Institute of Mental Health and Neurosciences (NIMHANS), Bangalore, India, docravi20@yahoo.com

Date of Submission: 10-Apr-2010
Date of Decision: 10-Apr-2010
Date of Acceptance: 22-Jun-2010

Code Number: ni11078

PMID: 21483137

DOI: 10.4103/0028-3886.79149

Sir,

Hot cross bun (HCB) sign is a cruciform hyperintensity in the pons best seen on axial T2-weighted and fluid attenuation inversion recovery (FLAIR) sequences of magnetic resonance imaging (MRI) of the brain. This sign is classically described in cerebellar type of multiple system atrophy (MSA-c). However, this sign has also been described in other conditions. ^{[1],[2],[3],[4],[5]} We report here, HCB in 2 patients of human immunodeficiency virus (HIV)-related progressive multifocal leukoencephalopathy (PML).

A 29-year-old woman and a 32-year-old man presented to us with asymmetrical cerebellar syndrome with pyramidal and bulbar dysfunction of subacute onset of 2 and 3 months duration, respectively. Cerebrospinal fluid (CSF) analysis showed elevated proteins, 600 mg/dL and 550 mg/dL, respectively, and positive polymerase chain reaction (PCR) for JC virus. HIV serology was positive in both the patients with a CD4+ T-cell count of 136/μL and 156/μL, respectively.

MRI of brain, multiplanar T1, T2, FLAIR, diffusion, and postcontrast imaging done on 3T MRI system showed the classical HCB sign in both the patients [Figure - 1] and [Figure - 2]. Magnetic resonance spectroscopy (MRS) revealed gross reduction of N-acetyl aspartic acid (NAA) with NAA/creatine (Cr) ratio of 0.33 and 0.56 in the cerebellar hemisphere bilaterally. Choline (Cho) was mildly elevated with Cho/Cr ratio of approximately 1.1 and 1.5, respectively.

HIV-related PML presents with usually clinical features of limb weakness, cognitive deficits, speech or visual deficits, ataxia, and less commonly with seizures and headache. ^[6] The chances of development of HIV-related PML correlates with low CD4 count. ^[7] Both our patients had a presentation with predominantly asymmetrical cerebellar ataxia, speech deficits, limb weakness, low CD4 count (less than 200/μL) and nonenhancing lesions in MRI scan. They were detected to be positive for JC virus PCR, thus confirming the diagnosis of HIV-related PML. Usually, PML affects periventricular and subcortical frontal and parieto-occipital white matter followed by brainstem, cerebellum, thalamus, basal ganglia, corpus callosum, and rarely cervical and thoracic spinal cord. ^[7] MRS supported the PML diagnosis as the lesions showed a decreased NAA and Cr content, whereas choline-containing substances (Cho) and lactate were elevated. ^[7] Our patients had asymmetrical involvement of posterior fossa structures (cerebellum, pons, and midbrain) with signal change and atrophy with the HCB sign. In MSA-c, the degeneration of pontine neurons and loss of myelinated transverse pontocerebellar fibers with preserved tegmentum and corticospinal tracts has been cited as the main cause for this sign. ^[1] It was proposed that HCB sign is due to gliosis in addition to the loss of neurons. ^[2] HCB sign has also been observed in spinocerebellar ataxia (SCA) type 2 and 3. In a study of T2-weighted axial MRIs from 138 SCA patients, an overall frequency of HCB sign was 8.7%. Of these, 25.7% were SCA 2 and 1.3% were SCA 3. ^[3] The sign has also been described in a variant of Creutzfeldt Jacob disease and in a case of severe parkinsonian syndrome associated with cerebellar and brain stem dysfunction due to presumed vasculitis. ^[4],[5] We consider the HCB sign in our patients was also an end result of dying back phenomenon in the axons of various cerebellar connections along with degeneration of pontine neurons and pontocerebellar fibers with gliosis over months. Thus we conclude that PML is also one of the rare causes of HCB sign.

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