Radiological Diagnosis

Selective Corticospinal Tract Involvement in Acute Disseminated Encephalomyelitis

MRI shows selective involvement of corticospinal tracts seen as symmetrical hyperintensities in centrum semiovale, posterior limb of internal capsules [Figure - 1] cerebral peduncles [Figure - 2], basis points [Figure - 3] extending upto medulla. In view of paraparesis with UMN signs in upper limbs, cord disease was suspected. However to our surprise spinal cord MRI was normal, but brain MR showed lesions described as above. Considering preceding history of upper respiratory tract infection with pyramidal signs, CSF picture and MRI revealing symmetrical white matter hyperintensities, diagnosis of Acute disseminated encephalomyetitis (ADEM) was considered. Patients responded to intravenous dexamethasone dramatically and started walking and running on his own within 15 days of starting treatment. No recurrence or residual deficit has been reported at 1,3 and 6 months follow up.

ADEM is an immune mediated response to preceding viral infection or vaccination. It occurs in all ages, although most cases are reported in children and young adults. ADEM has an abrupt onset and a monophasic course[1]. Neurologic symptoms characteristically begin 1 to 3 weeks after viral usually upper respiratory infection and includes encephalopathy, motor deficit, bilateral optic neuritis, ataxia and rarely aphasia[2].

Multifocal, widely distributed, typically bilateral but asymmetric hyperintense lesions are usually seen in subcortical while matter but deep white matter, thalami, brain stem and cerebellum can also be affected[3]. Lesions may be small punctate to large in size and typically show prompt regression in response to steroid therapy. Site restricted or selective lesions are of rare occurrence in ADEM[4] as noticed in present case.

Hyperintense lesions involving corticospinal tract can also occur in leukodystrophies e.g. adrenoeukodystrophies metachromatic leukodystrophies[5] and amyotropic lateral sclerosis. Leukodystrophies can be excluded by clinical presentation (insidious onset with progressive down hill course) and associated characterstic MRI findings of diffuse confluent high signal in periventricular white matter. Armyotropic lateral sclerosis occurs in adults and again has chronic disease course[6].

To conclude, uncommon or rare neuroradiologic observations require interpretation in clinical context so as to have index of suscipion for treatale disorders like ADEM if recognized in time.