Mitochondrial leukoencephalopathies: A border zone between acquired and inherited white matter disorders in children?

BACKGROUND:There is emerging evidence implicating mitochondrial dysfunction in the pathogenesis of acquired demyelinating disorders such as multiple sclerosis. On the other hand, some of the primary mitochondrial disorders such as mitochondrial leukoencephalopathies exhibit evidence of neuroinflammation on MRI. The inter-relationship between mitochondrial disorders and episodic CNS inflammation needs exploration because of the therapeutic implications. OBJECTIVE:We sought to analyze the clinical course and MRI characteristics in a cohort of patients with mitochondrial leukoencephalopathy to determine features, if any, that mimic primary demyelinating disorders. Therapeutic implications of these findings are discussed. PATIENTS AND METHODS:Detailed analysis of the clinical course, magnetic resonance imaging findings and therapeutic response was performed in 14 patients with mitochondrial leukoencephalopathy. The diagnosis was ascertained by clinical features, histopathology, respiratory chain enzyme assays and exome sequencing. RESULTS:Fourteen patients [Age at evaluation: 2-7 yrs, M: F-1:1] were included in the study. The genetic findings included variations in NDUFA1 (1); NDUFV1 (4); NDUFS2 (2); LYRM (2);MPV17(1); BOLA3(2); IBA57(2). Clinical Features which mimicked acquired demyelinating disorder included acute onset focal deficits associated with encephalopathy [10/14, 71%], febrile illness preceding the onset [7/14, 50%] unequivocal partial or complete steroid responsiveness [11/11], episodic/ relapsing remitting neurological dysfunction [10/14, 71%] and a subsequent stable rather than a progressive course [12/14, 85%]. MRI characteristics included confluent white matter lesions [14/14, 100%], diffusion restriction [11/14,78.5%], contrast enhancement [13/13,100%], spinal cord involvement [8/13,61.5%], lactate peak on MRS [13/13] and white matter cysts [13/14, 92.8%]. CONCLUSION:Clinical presentations of mitochondrial leukoencephalopathy often mimic an acquired demyelinating disorder. The therapeutic implications of these observations require further exploration.