Hypokalaemic periodic paralysis is a rare life-threatening syndrome but is potentially reversible when detected at an early stage. It can be divided into familial hypokalaemic periodic paralysis (FHPP) and HTPP. FHPP is more common in western countries and in paediatric patients.7
However, HTPP is an acquired form of hypokalaemic periodic paralysis and is most common in Asian men in their thirties.8
It is rarer in Caucasians or African-Americans and, therefore, can be difficult to recognise in such populations. Patients with HTPP exhibit acute recurrent episodes of flaccid paralysis, affecting the proximal muscles of the lower limbs, either following strenuous physical activity or a carbohydrate-rich meal.9
However, it has also been described to affect respiratory muscles resulting in respiratory distress.10
Also, studies have found that attacks of HTPP happen more frequently at night.11 12
There are a few theories behind the pathophysiology of HTPP but it is thought that in hyperthyroid patients there is an increase in the number and activity of Na/K ATPases of cell membranes, which is responsible for the refractory state of the sarcolemma and the transmembrane potassium shifts.8
It is inherited in an autosomal dominant pattern.7
Lab findings in HTPP include hypomagnesaemia and hypophosphataemia, which helps distinguish it from FHPP.
Correction of hypokalaemia is the treatment priority when it is severe. Control of the thyrotoxicosis with antithyroid drugs is essential. Blocker treatment may be helpful and can be used to prevent recurrent attacks of HTPP.13
In the acute management of hypokalaemia, intravenous potassium infusions might be insufficient to resolve acute attacks and intravenous propranolol has been reported to reverse attacks of weakness in patients unresponsive to potassium replacement.14
Potassium levels should always be monitored regularly as rebound hyperkalaemia can occur. Restoration of euthyroidism eliminates thyrotoxic attacks but HTPP can recur if thyrotoxicosis returns.
Hypokalaemic periodic paralysis is a rare disorder with recurrent periods of hypokalaemic paralysis between periods of normal serum potassium levels. In most cases, it is due to an abnormality in the 1 subunit of the dihydropyridine-sensitive calcium channel in the skeletal muscle. How a defect in a calcium channel produces hypokalaemic paralysis is not well understood.6
Although rare, there have been increasing cases of HTPP reported in European populations1–5
as well as some cases reported in children.7
With the effects of migration, there is an increasing need for doctors in the UK to be aware of HTPP and to include this in their differential diagnosis when faced with patients with hypokalaemia. For example, HTPP has been reported in Asian patients in Australia.15
- Hypokalaemic thyrotoxic periodic paralysis (HTPP) should be in the list of differential diagnoses for the acute care physician who is presented with acute tetraparesis in a patient with preserved consciousness.
- The treatment priority for HTPP is to correct the potassium deficit first in cases of severe hypokalaemia. In less severe cases, blocker treatment can be used during early treatment with antithyroid drugs until the patient is euthyroid.