Clinical features central to a myopathy associated with hypothyroidism include:
- muscular pains
- cramps, not necessarily associated with weakness
- slowed muscle relaxation, most clearly seen following a tendon jerk
The delay in relaxation is not due to repetitive muscle excitation - as in myotonia - but is probably the result of a reduced rate of cross-bridge uncoupling.
There may be frank muscle weakness in some patients, and the muscles may be firm to palpation and enlarged.
Investigations reveal a raised creatine kinase and fibre atrophy seen on muscle biopsy.
Last reviewed 01/2018