Neuronal intermediate filament inclusion disease (NIFID) is a neurodegenerative disorder of a heterogeneous clinical phenotype, encompassing behavioural changes, language impairment, perseveration, executive dysfunction with or without early onset dementia, extrapyramidal features, and subclinical or clinical involvement of upper and lower motor neurons, with age at onset of reported cases ranging from 23 to 56 years (table 1).1–5 NIFID was initially characterised neuropathologically on the basis of intraneuronal cytoplasmic inclusions of variable morphology which immunostained for all class IV intermediate filament (IF) proteins, namely NF-H, NF-M, NF-L and alpha-internexin.1–3 5 More recently it has been shown that a much larger proportion of the inclusions in NIFID are immunoreactive with the fused in sarcoma (FUS) protein than with IF,6 leading to changes in the suggested nomenclature.7 8 We present a further case demonstrating the broad phenotypic features, overlapping with both corticobasal degeneration and motor neuron disease.

A 62-year-old right-handed woman presented with a 2-year history of progressive difficulty with coordination and balance. She noticed weak grip and poor coordination in her right hand when playing tennis and had difficulty assembling familiar scuba diving equipment. She developed involuntary twitching of the fingers in the right hand and heaviness in the right arm. Over the next few months asymmetric leg weakness (right > …