Differential diagnosis of white matter diseases in the tropics: An overview

Abstract

In hospitals in the tropics, the availability of magnetic resonance imaging (MRI) facilities in urban areas and especially in teaching institutions have resulted in white matter diseases being frequently reported in a variety of clinical settings. Unlike the west where multiple sclerosis (MS) is the commonest white matter disease encountered, in the tropics, there are myriad causes for the same. Infectious and post infectious disorders probably account for the vast majority of these diseases. Human immunodeficiency virus (HIV) infection tops the list of infective conditions. Central nervous system (CNS) tuberculosis occasionally presents with patchy parenchymal lesions unaccompanied by meningeal involvement. Human T cell leukemia virus (HTLV) infection and cystic inflammatory lesions such as neurocysticercosis are important causes to be considered in the differential diagnosis. Diagnosing post infectious demyelinating disorders is equally challenging since more than a third of cases seen in the tropics do not present with history of past infection or vaccinations. Metabolic and deficiency disorders such as Wernicke's encephalopathy, osmotic demyelinating syndrome associated with extra pontine lesions and Vitamin B12 deficiency states can occassionaly cause confusion in diagnosis. This review considers a few important disorders which manifest with white matter changes on MRI and create diagnostic difficulties in a population in the tropics.

Keywords: Demyelinating disorders; white matter diseases.

Figure 1

26 year male presented with acute onset paraparesis, retention of urine, and disorientation. One month earlier he had right focal motor seizures with transient post ictal weakness for which he had been investigated elsewhere with no details. MRI brain [Figure 1A] on T2W images showed large hyperintense lesions in the temporal and parietal subcortex on the right side with scattered small hyperintense lesions predominantly in subcortical white matter of the opposite hemisphere. MRI of the spinal cord [Figure 1B] on T2W images showed liner hyperintense lesion in the dorsal cord which enhanced moderately following intravenous contrast. He was HIV positive and succumbed shortly thereafter.Autopsy of the brain lesion confirmed the clinical diagnosis of progressive multifocal leucoencephalopathy

Figure 2

A 52 year old woman was investigated for headache and recent onset seizures. Her MRI of the brain showed three discrete hyperintense lesions in the right frontal, temporal and parietal subcortex which enhanced on contrast. Biopsy of the larger lesion revealed dense lymphocytic infilteration with scattered foci of plasma cells, epitheloid cells and Langerhan's giant cells and surrounding gliosis. A repeat MRI done 3 months after starting anti tuberculous therapy showed resolution of lesions

Figure 3

(A and B) 31 year old male presented with three episodes of recurrent myelitis interspersed with one episode of optic neuritis over a period of 18 months. Initial MRI brain was normal. MRI of the cervical cord showed (Fig. 3A) on T2 W image, a linear contiguous lesion spanning more than 3 vertebral segments suggestive of longitudinally extensive transverse myelitis. On his fourth hospital admission, he presented with headache, disorientation and worsening of lower limb power. MRI brain (Fig. 3B) showed large lumpy posteriorly situated subcortical lesions.

Figure 4

One week after a febrile illness, a 55 year old man developed neurogenic dysphagia accompanied by ataxia and drowsiness. Clinical examination revealed ophthalmoplegia, cerebellar signs and sluggish deep tendon reflexes. MRI of the brain showed a single hyperintense lesion in the pons, On T2 W images which moderately enhanced with contrast. He rapidly recovered following intravenous steroids

Figure 5

(A and B) 18 year old male was admitted with progressive parapalegia of 3 months duration. Earlier in the year he had similar weakness which improved partially when he was admitted to a local hospital for fever and upper respiratory infection (review of old prescriptions revealed that he had received vitamin supplements). Clinically he was anemic and had hyper pigmentation of distal extremities (Fig. 5A). Peripheral smear and bone marrow confirmed the diagnosis of megaloblastic anemia. MRI of the spinal cord (Fig. 5B) showed on T2W images, linear hyperintense lesion in the cervical and upper dorsal cord sparing the anterior column. He improved moderately with Vitamin B12 therapy

Figure 6

A 24 year old male presented with acute onset headache with drowsiness in the background of recent fever. On examination he had pupil sparing ptosis, vertical gaze paresis, mild sensory neural deafness and bilateral subtle pyramidal signs. MRI brain showed symmetric hyperintense lesions in the caudate nuclei and putamina extending into the thalami and periaqueductal regions, on T2W images (Figure 6). His serum and CSF lactic acid levels were raised.A quadriceps mucle biopsy revealed subsarcoplasmic accumuilation of mitochondria) associated with cytochrome oxidase negative fibres. No mitochondrial mutations were detected. Following intravenous Thiamine therapy he recovered rapidly