Insulin-mediated hypokalemia and paralysis in familial hypokalemic periodic paralysis.

To elucidate a potential role for insulin-mediated extra-renal potassium disposal in the clinical syndrome of hypokalemic periodic paralysis, an obese affected man was studied using the euglycemic insulin clamp, which, in normal and obese subjects, produces predictable, insulin dose-dependent declines in plasma potassium levels. During a 20 mU/m2/minute euglycemic clamp (insulin level, 88 microU/ml) procedure, while the patient with hypokalemic periodic paralysis demonstrated severe resistance to insulin-mediated glucose uptake (glucose uptake 50 percent of that of normal control subjects, n = 17), his plasma potassium declined to a degree similar to that seen in normal subjects. During a subsequent higher dose, 200 mU/m2/minute insulin infusion (insulin level, 914 microU/ml), plasma potassium declined to 2.5 meq/liter, a value significantly below that seen in normal (n = 19) (3.3 +/- 0.1 meq/liter) and obese (n = 6) (3.2 +/- 0.1 meq/liter) subjects. During this study, paralysis began in the patient's hand and forearm at the potassium nadir and lasted three hours, despite restoration of normokalemia 30 minutes after paralysis began. Glucose disposal rates during this high-dose insulin infusion were one-half that seen in lean control subjects (n = 19) and similar to those in obese control subjects. If these findings are representative of hypokalemic periodic paralysis and can be generalized to larger numbers of patients, they indicate several new features of this syndrome. The ability of insulin to induce hypokalemia is enhanced in this syndrome even in the presence of marked coexistent obesity-related resistance to the action of insulin to promote glucose utilization. Enhanced sensitivity of potassium uptake systems to activation by insulin (and other factors) may be a central feature of this syndrome. Additionally, paralytic hypokalemia can be induced during a euglycemic insulin clamp procedure, which could be utilized as a diagnostic test for this syndrome.