We describe a 72 year old woman who presented with a 5 year history of progressive gait uncertainty, frequent sudden falls, and difficulty rising from a chair, associated with fatigue. She noticed some degree of distal weakness in her arms when carrying weight compared with previous years. She had no complaints of pain or cramps but noticed stiffness and ‘locked’ legs when walking. She denied cranial nerve problems and had no general systemic complaints. Past medical history was significant for hypertension. Family history was unremarkable.

Examination revealed normal vital signs and intact cranial nerves. Slow and slightly slurred speech was evident. Her trunk was forcefully bent forwards in a camptocormic attitude, which could be corrected by passive extension of the trunk. Her tone was increased with rigid wrist and hips and brisk (3+) reflexes and an equivocal bilateral extensor toe sign. Her gait was slow, and worsened during the day and over time to the extent that it limited everyday activities and often culminated in sudden falls. Pendular movements were reduced on the left. She had mild weakness in the shoulder abductors (4), finger flexors (4.5), hip flexors (4), and ankle dorsiflexors (4). Sensory examination and coordination were normal.

Routine blood investigation …