Very rarely, people with hypothyroidism develop a painful condition of the muscles. This condition, myotonia, results in pain, cramping, and weakness. It may affect the proximal muscles of the arms or the legs.
In these conditions, a peculiar exam finding may be made. Tapping the muscle with a reflex hammer can cause a ridge of muscle contraction, referred to as myoedema. In some cases, thickening of the muscles occurs due to fluid retention or the deposition of connective tissue.
Treatment of hypothyroidism with thyroid supplements is normally helpful for thyroid-related muscle diseases.
Other illnesses that may affect the muscles include:
Adrenal gland, pituitary gland, parathyroid gland problems, exposure to toxins or certain medicines, and diseases of nutrition or metabolism