Alterations in somatosensory, visual and auditory pathways in amyotrophic lateral sclerosis: an under-recognised facet of ALS.

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While amyotrophic lateral sclerosis is widely recognised as a multi-network disorder with extensive frontotemporal and cerebellar involvement, sensory dysfunction is most of the time denied as "ALS is a motor neuron disease", despite the wide reports of pain by patients and multiple MRI studies telling degeneration in many areas in the brain. This study complements the work in this area, hopefully many progress could be expected when scientists will stop to think of ALS as only "a motor neuron disease".

In a prospective neuroimaging study the authors have systematically evaluated cerebral grey and white matter structures involved in the processing, relaying and mediation of sensory information. Twenty two C9orf72 positive Amyotrophic Lateral Sclerosis patients, 138 C9orf72 negative Amyotrophic Lateral Sclerosis patients and 127 healthy controls were included.

Widespread cortical alterations were observed in C9+ Amyotrophic Lateral Sclerosis including both primary and secondary somatosensory regions. In C9- Amyotrophic Lateral Sclerosis, cortical thickness reductions were observed in the postcentral gyrus.

Thalamic nuclei relaying somatosensory information as well as the medial and lateral geniculate nuclei exhibited volume reductions. Diffusivity indices revealed posterior thalamic radiation pathology and a trend of left medial lemniscus degeneration was also observed in C9- Amyotrophic Lateral Sclerosis.

The authors' radiology data confirm the degeneration of somatosensory, visual and auditory pathways in Amyotrophic Lateral Sclerosis, which is more marked in GGGGCC hexanucleotide repeat expansion carriers.

In contrast to the overwhelming focus on motor system degeneration and frontotemporal dysfunction in recent research studies, authors' findings confirm that sensory circuits are also affected in Amyotrophic Lateral Sclerosis.

The involvement of somatosensory, auditory and visual pathways in Amyotrophic Lateral Sclerosis may have important clinical ramifications which are easily overlooked in the context of unremitting motor decline.

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