Case Reports

Symptoms Mimicking Those of Hypokalemic Periodic Paralysis Induced by Soluble Barium Poisoning

An investigation of a patient who presented with apparent hypokalemic periodic paralysis instead revealed barium poisoning.

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Hypokalemic periodic paralysis (HPP) is a relatively common and potentially life-threating condition that can be either sporadic or recurring and has both inherited and acquired causes. 1 Familial HPP, on the other hand, is a rare condition (1:100,000) caused by loss of function mutations leading to the disruption of membrane potential consequently making them inexcitable. 2 Appearance of symptoms is typically in the first or second decade of life (60% of cases have onset aged < 16 years) with susceptible individuals experiencing sudden onset of perioral numbness; weakness; centrifugal paralysis, often with nausea; vomiting and diarrhea; and prostration, usually triggered by highcarbohydrate meals and rest following sustained muscle-group use. 3

These symptoms are common to all forms of HPP, making the differential diagnosis wide and confusing. Rhabdomyolysis is occasionally associated with many severe hypokalemic episodes. 4 Myopathy and permanent muscle weakness have been reported in HPP. 5,6 Other reported inciting factors include a drop in serum potassium caused by β-adrenergic bronchodilator treatment. 7 Clinical attacks also have been associated with diabetic ketoacidosis and combined hypokalemia and hypophosphatemia. 8 Thyrotoxicosis also causes similar muscle action potential changes but only when hyperthyroidism is uncorrected. 9-12 Less commonly, hypothyroidism has been reported to be associated with hypokalemic paralysis. 3

Pa Ping, a condition involving hypokalemic paralysis of uncertain etiology, is geographically centered in the Szechuan region of China. 13 Cases of Bartter, Liddle, and Gitelman syndromes also have been associated with hypokalemic paralysis. 3,14 There is an association with malignant hyperthermia following or during systemic anesthesia. Patients presenting as Guillain-Barré syndrome have been found to have periodic paralysis triggered by hypokalemia from any cause. 15 Sjögren syndrome and renal tubular acidosis also are reported to have triggered symptoms of hypokalemic paralysis. 16,17

True type 1 HPP is caused by channelopathies resulting from mutations in the calcium channel gene CACN1AS (HypoPP1), which accounts for 70% of the cases, whereas type 2 HPP is cause by sodium channel gene SCN4A (HypoPP2) mutations, which accounts for 10% to 20% of cases. 18,19 An association with a voltage-gated potassium channel KCNE3 mutation has been made but is disputed. 20,21 Females typically have less severe and less frequent attacks, and attacks lessen or disappear during pregnancy. 22

In a small controlled trial, acetazolamide has been reported to have prophylactic benefit, although a more powerful carbonic anhydrase inhibitor, dichlorophenamide, was reported to be effective in a study after acetazolamide had become ineffective. 23,24 These treatments would not be expected to be of clinical use in hypokalemia due to barium poisoning.

Barium poisoning has been reported as a result of accidental contamination of foodstuffs with soluble barium. 25 Onset of symptoms is rapid, with nausea, vomiting, diarrhea, and malaise followed rapidly by weakness, which can include the muscles of respiration. This littleconsidered but rapidly lethal poisoning event can be accidental as a result of environmental exposure due to unintentional ingestion of the toxin or deliberate criminal poisoning as in this case. Because deliberate poisoning rarely crosses the mind of the clinician, awareness of the potential similarity of barium poisoning to other forms of HPP and even familial HPP is important.

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