A 74-year-old man was hospitalised in January 2021 because he developed in few days a severe muscle weakness associated with ascending numbness in the four limbs. His medical history only included a pulmonary embolism in 2016 and myelodysplastic syndrome (MDS) with multilineage dysplasia diagnosed in 2019, with low risk score according to the Revised International Prognostic Scoring System classification.
Initial neurological examination showed a symmetrical proximal and distal quadriparesis associated with distal hypoesthesia in all four limbs and diffuse areflexia. Motor testing revealed a deltoid and biceps brachii deficit of MRC grade 3/5 and a first dorsal interosseous deficit of 2/5. In the lower limbs, psoas and quadriceps muscle testing were graded 3/5.
Nerve conduction studies (NCS) revealed prolonged distal motor latencies and increased duration of the compound motor action potential (CMAP) in bilateral ulnar, median, tibial and common peroneal nerves. Conduction blocks were present in the forearm on both…