The March 15, 2022, session of Duke Medicine LEADS featured Tyler Couch, MD, and John Roberts, MD presenting on "A Mysterious Case of Recurrent Muscle Cramping."
Pearls
- An approach to patients with hypokalemia can be broken down into etiologies secondary to low intake, losses (both renal and extrarenal) and transcellular shifts. An alternative approach can start with the acid/base status in the setting of hypokalemia, where renal tubular acidosis (RTA) type 1 and 2 and lower GI losses are found in acidotic states, upper GI or renal loss of chloride rich fluid are seen in alkalotic states and hypomagnesemia or cellular shifts can be causes of hypokalemia when the pH is normal.
- A basic approach to acid/base disorders including checking the anion gap and expected compensation is essential in a comprehensive assessment of electrolyte derangements.
- Differential diagnoses discussed in this case included:
- Renal potassium wasting in the setting of non-reabsorbable anions secondary to alcoholic ketoacidosis, which is worsened by accompanying volume (and chloride) depletion. In the nephron, when there is less distal chloride present and more non-reabsorable anions (like bicarbonate or ketoacids), then there is a stronger negative lumen potential difference and thus, accelerated potassium secretion in the collecting duct.
- Gitelman syndrome, an autosomal recessive genetic disorder affecting 1:40,000 individuals via defects in NaCl cotransporter in the distal tubule resulting in signs and symptoms that mimic the effects of persistent thiazide diuretic use including renal potassium wasting, hypomagnesemia, metabolic alkalosis and hypocalcuria.
- Bartter syndrome is a group of autosomal recessive genetic disorders affecting 1:100,000 individuals via defects in the Na-K-2Cl cotransporter or other channels in the ascending limb of Henle. Bartter syndrome also features hypokalemic, metabolic alkalosis, but unlike Gitleman syndrome presentation is usually earlier in life, urine calcium is increased or normal and hypomagnesemia is not always present.
- Hypokalemia Periodic Paralysis is caused by either inherited autosomal dominant mutations in muscle ion channels or can be acquired in association with thyrotoxicosis. Symptoms are typically intermittent often after exercise or strenuous activity.
Duke Medicine Learning, Education, and Discussion Series (LEADS) takes place each Tuesday at 12 p.m. Learn more and see schedule of upcoming sessions.