Amyotrophic lateral sclerosis with demyelinating neurophysiology and a motor band sign

We describe an unusual case of clinical amyotrophic lateral sclerosis (ALS) with initial neurophysiological studies suggesting demyelination, along with neuroimaging findings that helped to support the eventual diagnosis. An otherwise well 68-year-old man had 8 weeks of left upper limb weakness. On examination, there were widespread lower and upper motor neurone findings suggesting ALS. However, nerve conduction studies identified sensorimotor demyelinating changes suggesting chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), a diagnosis further supported by cerebrospinal fluid analysis. MR scan of the brain revealed a 'motor band', a feature seen commonly in ALS. His condition was refractory to immunotherapy with clinical progression in-keeping with ALS, establishing the diagnosis. ALS is rarely associated with demyelinating neurophysiological changes resembling CIDP. The clinical phenotype is crucial to support the correct diagnosis and imaging findings may help.