Baló’s concentric sclerosis

A 40-year-old woman presented with tingling over the right side of her head and swaying to the right side while walking for two months. She had altered sensorium two months back, which had improved after administering methylprednisolone. However, she again presented with altered sensorium after three weeks.

MRI Brain (Figures 1 to 3) shows multiple round to oval, bilateral asymmetrically distributed lesions in the periventricular and deep white matter, right thalamus, right frontal subcortical region, pons and medulla. These lesions are hyperintense on T2/FLAIR weighted images with central hypointensity, giving it a bull's eye/onion ring appearance. The lesions are hypointense on T1-weighted images with a peripheral rim of restriction on diffusion-weighted images. Compared to the scan performed one and a half months back (Figure 4), there is an increase in the number and size of the lesions.

Background

Baló's concentric sclerosis is a rare demyelinating disease previously considered to exhibit a fatal monophasic course. It was first described in 1906 by Sir Otto Marburg. But became widely known after 22 years when Sir Josef Baló published a case report of right hemiparesis and optic neuritis, whose autopsy revealed demyelinated lesions, which was described as encephalitis periaxialis concentrica. The clinical course of Baló's concentric sclerosis can be classified into the following types: monophasic, relapsing-remitting, and primary progressive [1]. Recent reports show extended survival, spontaneous remission, and asymptomatic cases. Some consider it a variant of Multiple sclerosis, while others consider it a discrete pathology [2,3].

Clinical Perspective

Patients generally present with signs of focal neurological deficit. It was earlier observed that patients with Balo’s concentric lesions have a rapid course but respond to high-dose steroids. Recent studies speculate that it is a heterogeneous disease in which one subgroup shares common features with Multiple sclerosis (humoral responses) and another subgroup is characterised by a different etiopathogenesis (activated macrophages and astrocytes)[4]. Unlike Multiple sclerosis, oligoclonal bands are rarely seen in the CSF of patients with Baló's concentric sclerosis. Such concentric lesions have been reported in neuromyelitis optica and neuromyelitis optica spectrum disorder[5,6,7]. Additionally, they have been reported in patients with progressive multifocal leukoencephalopathy, CADASIL[8], intravenous drug use, hepatitis C, and human herpes virus 6[9].

Imaging Perspective

T1-weighted MR imaging shows alternating isointense and hypointense concentric rings in the white matter, with hyperintense lamellae on T2-weighted sequences. They represent alternating layers of myelinated and demyelinated neurons (Figure 5) [7]. The distinctive appearance helps differentiate it from the tumefactive demyelinating lesions and lesions of conventional multiple sclerosis. Tumefactive lesions are more than 2cm with a ring/open ring enhancement without layering. High signal intensity can be seen at the periphery of lesions on diffusion-weighted imaging sequences. On Gadolinium administration, the lesions show peripheral enhancement, but occasionally enhancement of multiple layers occurs.  Unlike conventional multiple sclerosis, lesions occur predominantly in the cerebral white matter and tend to spare the subcortical U-fibers.

Outcome

It is an uncommon entity with varied clinical course, some of the patients having poor outcome. Hence, early identification on MRI is essential. Patients are often treated with high-dose glucocorticoids, plasma exchange and disease-modifying agents. 

Take Home Message

Baló's concentric sclerosis was previously considered a rare disease with poor outcome. However, extensive research in the past few years has considered it to exhibit varied clinical course. Imaging is vital for diagnosing Baló's concentric lesions, thereby guiding further management.