Occasional essay: Upper motor neuron syndrome in amyotrophic lateral sclerosis

What is it about?

Upper motor neuron signs are required for the clinical diagnosis of ALS. However clinical evidence of UMN involvement in suspected ALS is often difficult to elicit, using the classical signs of the UMN syndrome hallowed by generations of clinical teaching. A historical analysis reveals that the generally accepted features of the UMN syndrome rely on uncertain and unvalidated assumptions. Review of the motor disorder in ALS and ALS-FTLD from clinical, neuropathological, and neuroimaging perspectives implies that the motor features reflect not only corticospinal tract deficits, but abnormalities distributed more widely in the descending motor system and its interconnexions with basal ganglia and cerebellum, and through the corpus callosum. These cause higher-order deficits of motor function that, with prominent coincidental lower motor neuron abnormalities, may overwhelm traditional corticospinal deficits, if present. We show that ALS is a syndrome of frontal brain degeneration with complex higher-order motor and executive dysfunction. Assessment of these motor and cognitive deficits should address these hitherto neglected aspects using neurophysiological, neuropsychiatric and neuroimaging techniques. In ALS the current clinical emphasis on the traditional neurological concept of the UMN lesion is insensitive and misdirected.

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