Diagnosis

A free workbook to download for those who are in the diagnostic process, contains information on each type of PP, diagnostic testing, available therapies, how to determine episode triggers and  work out a management plan. download here

The normal renal response when hypokalemia is due to non-renal causes is a TTKG <2, where a TTKG >5 is indicative of increased secretion of K+ in the cortical collecting ducts. Thus a transtubular potassium concentration gradient (TTKG) of greater than 3.0 indicates hypokalemia of renal origin, while a value below 2.0 indicates intracellular shift of K+, as found in ion channelopathy hypokalemic periodic paralysis.

This chart allows comparison of the forms of primary periodic paralysis, symptoms, clinical and cardiac signs, effect of potassium, triggers and therapies. 

When evaluating patients for periodic paralysis it is vital to obtain accurate results from blood draws. Because potassium levels which vary only a fraction of a point may be enough to trigger weakness in some patients, the lab may need to be made aware of specialized procedures which should ideally be used to obtain samples for K+ evaluation.

From "A Manual of Laboratory Diagnostic Tests" by Frances Fischbach, Page 247-253.

Potassium (K+) Normal Values: 3.5-5.0 mmol/liter 4.0-4.7 mmol/liter (average)

What happens during an attack of Periodic Paralysis?

People with Periodic Paralysis (PP) have episodes in which their muscles become weak or paralyzed in response to variations in the amount of potassium in their blood. These variations occur during sleep, they may result from food the person has eaten, from a sudden change in a person's activity level, from rest after activity, emotional stress, from becoming chilled, or a number of other factors. Potassium levels vary all the time.