Document resource
A woman in her 60s had a 10-year history of painless, slowly progressive weakness in both hands, which caused difficulties with daily manual household tasks. Over the previous 6 months, she had also had pins and needles along the medial aspect of both hands and forearms. She was a retired primary school teacher. On examination, there was bilateral intrinsic hand muscle wasting (figure 1). Nerve conduction studies showed characteristic compound motor action potential findings of greater attenuation in abductor pollicis brevis than in abductor digiti minimi.1 Median sensory nerve action potentials (SNAPs) were relatively preserved while ulnar and medial antebrachial cutaneous SNAPs were absent bilaterally. This suggested a compression or irritation of the lower plexus from below, as T1 sensory and motor nerve fibres were affected disproportionately to C8 fibres, in keeping with the structural organisation of these fibres in the lower trunk. MR scan of the brachial plexus supported this anatomical localisation, showing bilateral C7 cervical ribs that contacted both inferior trunks from below, causing focal neural enlargement and abnormal STIR (short-tau inversion recovery) hyperintensity (figure 2).