About Thyrotoxic Myopathy
The primary cause of thyrotoxic myopathy is hyperthyroidism, a condition where the thyroid gland produces too much thyroid hormone (thyroxine). This excess hormone disrupts muscle function and the way nerves and muscles communicate, making it a neuromuscular disorder. Common causes of hyperthyroidism that lead to this condition include:
- Graves’ disease (the most common cause of hyperthyroidism)
- Toxic multinodular goiter or thyroid adenomas (less common causes of hyperthyroidism)
Non-modifiable risk factors for thyrotoxic myopathy cannot be changed or controlled. These include
- Increasing age
- Genetic predispositions like a positive family history of related conditions
On the other hand, modifiable risk factors for thyrotoxic myopathy can be influenced or changed. These include:
- Unhealthy eating habits
- Lack of exercise
- Other lifestyle choices, which can be shaped by cultural and social factors
Making changes like maintaining a healthy weight, being physically active, and following a nutritious diet can help reduce the impact of modifiable risk factors on thyrotoxic myopathy.
The most common early symptoms of thyrotoxic myopathy include:
- Muscle weakness
- Myalgias (muscle tenderness)
- Wasting of the pelvic girdle and shoulder muscles: Muscles around the hips (pelvic girdle) and shoulders become weak and shrink
- Fatigue
- Heat intolerance
As thyrotoxic myopathy progresses or reaches higher severity levels, other common symptoms that may occur include:
- Rhabdomyolysis (acute muscle breakdown)
- Damage to the muscles controlling eye movement
- Temporary episodes of severe muscle weakness associated with low blood potassium levels (known as periodic paralysis)
- Additionally, individuals may experience symptoms such as weight loss, tremors, palpitations, excessive sweating, nervousness, sleep disturbances, and in rare cases, psychiatric symptoms like psychosis or mania.
Doctors use various exams and tests to diagnose thyrotoxic myopathy. The common ones include:
- Physical exam: The healthcare professional may look for:
- Muscle weakness, especially in the shoulders and hips,
- Symptoms of hyperthyroidism, such as rapid heartbeat, hand tremors, or warm, moist skin
- Signs of muscle wasting (shrinking muscles) in the pelvic or shoulder areas
- Blood tests:
- TSH (thyroid-stimulating hormone): Low levels may indicate hyperthyroidism
- Free T4 (free thyroxine) and Free T3 (free triiodothyronine): These tests measure thyroid hormones levels, which are usually high in hyperthyroidism.
- Imaging tests:
- Radioactive iodine scintigraphy: This test shows how much iodine the thyroid absorbs, helping to confirm hyperthyroidism and identify its cause
- Thyroid blood flow via ultrasonography: This test uses sound waves to check for increased blood flow in the thyroid, a sign of overactivity.
To determine the severity of thyrotoxic myopathy, doctors may perform further examinations and tests.
- Resting heart rate check: A resting heart rate over 90 beats per minute is common in hyperthyroidism and may help indicate the severity of thyrotoxic myopathy, especially if cardiovascular (heart) disease is also present.
- Heart evaluation: The heart may be checked to determine the severity of thyrotoxic myopathy, especially if there are signs of heart problems like a rapid heart rate or irregular rhythm. Tests like a heart ultrasound (echocardiogram) can help assess the heart’s health and identify complications caused by the condition.
- Imaging tests: In severe cases, imaging tests like MRI (magnetic resonance imaging) scans, CT (computed tomography) scans, or PET (positron emission tomography) scans may be used to look for muscle or organ damage caused by complications.
The main goals of treating thyrotoxic myopathy are to reduce circulating thyroid hormone levels and block the peripheral effects of these hormones.
Here are the treatment options:
- Medication
- Beta-blockers: These help control symptoms like rapid heart rate and tremors by blocking the effects of thyroid hormones on the heart.
- Antithyroid medications: Drugs like methimazole or propylthiouracil reduce the production of thyroid hormones in the body.
- Therapeutic procedures aim to restore a normal thyroid hormone level and may involve radioactive iodine therapy or surgery.
- Radioactive iodine therapy: This treatment involves taking radioactive iodine, which is absorbed by the thyroid gland, gradually reducing its activity.
- Surgery (thyroidectomy): In cases where medications are not effective or suitable, surgical removal of part or all of the thyroid gland may be necessary.
- These treatments aim to reduce thyroid hormone production, block their effects on tissues like muscles, or directly target and lower the activity of the overactive thyroid gland.
- Lifestyle behavior changes such as maintaining a healthy diet, regular exercise, and managing stress can support overall treatment effectiveness.
Medication dosing may be affected by many factors. Check with your health care professional about dosing for your individual situation. Side effects can occur. Check with your health care professional or read the information provided with your medication for side effect information.