*A Diagnostic Flowchart for Diagnosing Hypokalemic Periodic Paralysis

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.

The transtubular K+ concentration ([K+]) gradient (TTKG) is calculated using the following formula: TTKG = [K+]urine/(urine/plasma)/osmol/[K+]plasma

A useful diagnostic flowchart  for diagnosing Hypokalemic Periodic Paralysis by comparing acid/base balance, amount of potassium excreted by the kidneys during an attack, and a few other factors.  

Patient’s History

Eliminate dietary inadequacy, diuretic, thyroid hormone or caffeine abuse, herbal usage (i.e. licorice root) or “body-building” supplements as potential causes of hypokalemia. 

Recent history of ?: Unusual intensity of exercise; high carbohydrate intake (inc. alcohol) ; stress or life crisis; chilling; or combination of these factors.

Signs consistent with hyperthyroidism or excess of beta-adrenergic activity; recent weight loss, diaphoresis, tachycardia, systolic hypertension, and wide pulse pressure.

Has patient experienced exercise intolerance, weakness or paralysis in past, especially on awakening? (Patients sometimes do not recognize exercise intolerance or paralysis on awakening as abnormal.)Family history: Family members, including cousins, aunts, uncles, grandparents with similar symptoms or unexplained weakness, exercise intolerance, late development of myopathy in legs?