About Thyrotoxic Periodic Paralysis (TPP)
A rare complication of hyperthyroidism (usually Graves’ disease), thyrotoxic periodic paralysis (TPP) was originally identified in in 1902 and has found to be most common amongst Asian populations who experience a 2% incidence of TPP in hyperthyroid patients as compared to 0.2% in non-Asian populations.
95% of cases occur in men.
The two main features of TPP are acute reversible episodes of muscle weakness lasting from a few hours to 3 days and decreased potassium levels in the blood (hypokalaemia). These conditions are connected as potassium is an important electrolyte for muscle and nerve functioning and in TPP the lower the potassium level the more severe the weakness.
In 80% of cases the first episode of TPP occurs between the age of 20-40 with a higher frequency of attack seen at night or early morning. There is also a seasonal variation with attacks more frequent in the summer months.
Commonly reported factors which precede attacks include high carbohydrate ingestion and strenuous exercise but also:
- Trauma
- Acute upper respiratory tract infection
- High salt diet
- Emotional stress
- Alcohol ingestion
- Use of drugs such as corticosteroids and non-steroidal anti-inflammatory drugs
Diagnosis
This is tricky as the initial symptoms of thyroid overactivity can be subtle and may precede the onset of the acute attack of TPP by months. They include:
- Weight loss
- Palpitations
- Heat intolerance
- Increased appetite
- Agitation
- Insomnia
- Hand tremors
- A fast heart rate
- Excessive sweating
The attack itself normally begins with muscle pain, cramps or muscle stiffness followed by weakness which begins in the upper leg muscles and can progress to both arms and legs. The bladder and bowel is not affected. Although there is complete recovery between episodes of weakness, the attacks can reoccur with intervals varying in individuals to days, weeks or months.
If the weakness involves muscles involved in swallowing or breathing this is a medical emergency and an ambulance should be called.
Diagnosis will depend both on the awareness of the condition and its association with thyrotoxicosis by the doctor, and a recognition of abnormalities in biochemical and ECG tests. There may also be a family history of the condition.
As several other conditions can result in low potassium levels it is important to differentiate the condition particularly to avoid too high a level of potassium replacement which will exacerbate the hypokalaemia.
The use of simple, fast, and inexpensive tests of blood and urine electrolytes, and acid-base status may aid in differentiating such disorders as supporting thyroid function tests may not always be immediately available.
Initial Treatment
Emergency treatment is necessary as the muscle weakness can extend to the heart - leading to life threatening conditions. Treatment doses of potassium chloride have to be minimised to avoid rebound rises in potassium levels and beta blockers can help to present the recurrence of hypokalaemia. Patients are also normally recommended to have a low carb low salt diet.
Ongoing Treatment
TPP responds well to treatment and taking beta blockers and avoiding factors which are known to precipitate attacks can minimise or even prevent attacks. Initially anti-thyroid drugs are required to reduce the elevated thyroid hormone levels. Early definitive management of the hyperthyroidism by radioiodine or thyroidectomy are recommended to avoid any future recurrence.
I hope you have found this helpful.
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