• CLINICAL NEUROLOGY

We all make mistakes but often remain oblivious to them until events conspire to inform us. We might uncover our own error after reviewing a patient on receiving a result that disproves our first impression, or hear about the error in far less palatable circumstances. At other times, we remain oblivious. Our diagnosis seemed to explain a patient’s condition but it was wrong. The correct diagnosis had not occured to us or had been discounted, and we erroneously interpreted investigations as supporting our incorrect diagnosis, our oversight remains hidden.

Barp et al describe just such an impasse.1 Two patients with myopathy had diagnostic journeys over many years, one labelled with limb-girdle muscular dystrophy, the other vasculitis. The authors who took over their care managed to identify a myositis-specific antibody—3-hydroxy-3-methylglutaryl–coenzyme A reductase autoantibody (HMGCR)—in both patients. In the appropriate clinical context this is a highly specific finding, occurring in a proportion of patients with autoimmune necrotising myopathy, a treatable condition comprising about 20% of idiopathic autoimmune myopathies.2

This was quite a coup—so what happened and how did they do it?

A clinical clue much beloved in neurology is the speed of onset of an illness. A slow progression over years indicates degenerative or genetic process. One of their patients had an isolated …