A 40 y.o woman comes to the office with progressive muscle weakness over the last 6 months. She finds it difficult to climb stairs and comb her hair, and she is unable to walk even short distances without rest. There is no associated muscle pain. The patient was diagnosed with hypothyroidism a year ago when she started gaining weight and has been taking levothyroxine since then. Four months ago, she developed acute back pain. X-ray at that time revealed demineralization of the vertebral bones. Temperature is 37 C (98.6 F), blood pressure is 155/100 mm Hg, pulse is 76/min, and respirations are 15/min. BMI is 32. Physical examination shows facial hirsutism and mild proximal muscle weakness in the extremities. The patient’s muscles are not tender on palpation, and no fasciculations are noted. Deep tendon reflexes and sensory examination are normal. TSH is normal. Which of the following is most likely responsible for this patient’s muscle weakness?
A. Electrolyte abnormality
B. Mitochondrial dysfunction
C. Motor neuron disease
D. Muscle atrophy
E. Muscle inflammation
F. Peripheral nerve demyelination
Ans: A. Electrolyte abnormality