Patients usually cite decreased exercise tolerance, increased fatigue, and difficulty completing certain tasks after six months of onset.
Muscle involvement has been reported to occur in about 80% of thyrotoxic patients (see section #Epidemiology), [7] and the most common causes of hyperthyroidism are Graves’ disease, toxic multinodular goiter, and autonomously functioning thyroid adenoma.
[8] Excess thyroxine is believed to bring about the onset of thyrotoxic myopathy and eventually cause the degradation of muscle tissue.
Scientists agree thyroxine brings about the degradation of muscle fibers specifically at the motor end plates of neuromuscular junctions.
[1] To understand how high levels of thyroxine can be toxic and lead to thyrotoxic myopathy physiologically, consider basic neuromuscular junction function.
Under normal circumstances, muscle contraction occurs when electrical impulses travel down descending axons from the brain or spinal cord towards the neuromuscular junction.
The axon terminal depolarizes and releases Acetylcholine (ACh), a neurotransmitter, which in turn stimulates the motor end plate (MEP) of the muscle fiber the nerve is innervating.
[citation needed] With the onset of TM due to thyroxine toxicity, there is evidence to suggest that structural changes in MEPs could lead to muscle fiber degradation, weakness, and fatigue.
If a patient develops significant to severe muscle degradation as a result of TM, a physical therapist may be consulted for rehabilitation.
[citation needed] The first choice involves using medications to alleviate the symptoms and reverse the damage by blocking the production of thyroxine from the thyroid gland.
[citation needed] One treatment option is the use of radioactive iodine which directly destroys the overactive thyroid gland.
While the onset of hypothyroidism is most common with radio-iodine treatment, the condition has been observed in patients treated with medication series and surgery.
Since these goiters enlarge the thyroid and can cause the patient to become physically disfigured surgical treatment can alleviate both the aesthetic and physiological effects simultaneously.
Patients who are diagnosed have a normal life expectancy and can ultimately lead healthy lives if proper treatment is administered.
Typically, once the over-production of thyroxine is corrected and thyroid function adequately reaches a level of homeostasis, patients begin to regain muscle strength in two to four months.
[citation needed] The onset of TM requires toxic levels of the thyroxine hormone due to overproduction by the thyroid gland.