A 70-year-old woman presented with increasing weakness and fatigue over 4 years. She had suffered motor problems from birth with hypotonia and delayed motor milestones. She walked abnormally in childhood but appeared to show some improvement at the age of 10 years, remaining ambulant throughout her life. She was seen by an eminent neurologist at the age of 15 years who documented a waddling gait, and after investigation she was given a diagnosis of “amyotonia congenita”. At the age of 43 years she was reviewed; there had been no significant progression but she reported being intermittently worse during menstruation. Examination at that point revealed mild weakness of eye closure, mild right-sided ptosis, weakness and some wasting of the periscapular muscles and hip flexors. Investigations revealed mildly raised serum creatine kinase (CK) level (twice normal) and a myopathic electromyogram (EMG). Mild fibre hypertrophy and absence of type 2B fibres were noted on muscle biopsy and she was thought to have a form of congenital myopathy.

However, from the age of 66 years she had increasing difficulty climbing stairs and could only walk for 60 m. She was unable to lift heavy objects or use her arms above her head, she had difficulty holding her head up, occasional choking and breathlessness on exertion and when lying flat. Examination revealed bilateral ptosis with little fatigability (fig 1), mild facial and neck weakness, and her tongue was weak and had a central furrow. There was no ophthalmoplegia. She had marked shoulder girdle weakness with some wasting and scapular winging. There was also marked weakness around the pelvic girdle; she walked with a waddling lordotic posture, was just about able to get out of a chair without using her arms and she could stand on her heels and toes. Her vital capacity was 80% of …