How is the condition diagnosed?

The healthcare provider often suspects familial periodic paralysis based on the person's history of the attacks and a family history of the condition. If an attack is witnessed, the provider can detect the muscle weakness. A blood potassium level may be done.

When attacks are too rare to witness, the healthcare provider may want to try to cause an attack. This involves giving glucose, a carbohydrate, to a person if the low potassium form of this condition is suspected. Those suspected of having the normal or high forms of this condition might be given potassium in an attempt to cause an attack.

Sometimes an electrocardiogram or ECG, a test that shows the electrical activity of the heart, may be abnormal during attacks. This is due to the abnormal potassium levels. A test called electromyography, or EMG, may also be done. This test looks at how well the nerves and muscles work.

A muscle biopsy may be done in some cases. This is a procedure in which a small piece muscle tissue is removed with a special needle. This piece, or biopsy sample, can then be sent to the lab for analysis. The muscle tissue is often slightly abnormal in this condition.