Magnetic resonance imaging detection of deep gray matter iron deposition in multiple sclerosis: A systematic review

Multiple sclerosis (MS) is a chronic inflammatory and neurodegenerative disease involving immune-mediated damage. Iron deposition in deep gray matter (DGM) structures like the thalamus and basal ganglia have been suggested to play a role in MS pathogenesis. Magnetic Resonance Imaging (MRI) imaging methods like T2 and T2* imaging, susceptibility-weighted imaging, and quantitative susceptibility mapping can track iron deposition storage in the brain primarily from ferritin and hemosiderin (paramagnetic iron storage proteins) with varying levels of tissue contrast and sensitivity. In this systematic review, we evaluated the role of DGM iron deposition as detected by MRI techniques in relation to MS-related neuroinflammation and its potential as a novel therapeutic target. We searched through PubMed, Embase, and Web of Science databases following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, against predetermined inclusion and exclusion criteria. We included 89 articles (n = 6630 patients), and then grouped them into different categories: i) methodological techniques to measure DGM iron, ii) cross-sectional and group comparison of DGM iron content, iii) longitudinal comparisons of DGM iron, iv) associations between DGM iron and other imaging and neurobiological markers, v) associations with disability, and vi) associations with cognitive impairment. The review revealed that iron deposition in DGM is independent yet concurrent with demyelination, and that these iron deposits contribute to MS-related cognitive impairment and disability. Variability in iron distributions appears to rely on a positive feedback loop between inflammation, and release of iron by oligodendrocytes. DGM iron seems to be a promising prognostic biomarker for MS pathophysiology.

Subacute Combined Degeneration of the Spinal Cord: A Consequence of Recreational Nitrous Oxide Use

A 21-year-old female presented to the hospital with worsening bilateral lower extremity weakness and sensory changes in the distal extremities following chronic nitrous oxide (N₂O) abuse. Laboratory and radiographic results were suggestive of subacute combined degeneration of the upper cervical and thoracic spinal cord in the setting of a normal vitamin B12 level of 374 pg/mL with an elevation in methylmalonic acid to 1.14 mcmol/L. She was diagnosed with a relative B12 deficiency and treated with supplemental vitamin B12, resulting in an improvement in symptoms. This case highlights the importance of considering relative vitamin B12 deficiency as a diagnosis in the setting of nitrous oxide use, regardless of measured vitamin B12 level.