Review Question - QID 220781

This otherwise healthy athlete who presents with muscle cramps, fatigue, weakness, and hyporeflexia, most likely has electrolyte abnormalities. The ECG showing flat T-waves and large U-waves suggests hypokalemia.

Hypokalemia occurs when a patient has decreased potassium levels in the bloodstream relative to normal parameters. Potassium helps carry electrical signals to cells in the body and is critical to proper signal transduction in nerve and muscle cells. In strenuous physical activity, potassium can be wasted as part of fluid loss, such as with sweating. Hypokalemia can result in a myriad of sequelae, including fatigue and muscle cramps. In severe hypokalemia, life-threatening symptoms such as paralysis, tetany, hyporeflexia, rhabdomyolysis, and arrhythmias may occur. The most common cause of death in severe hypokalemia is cardiac arrhythmia (torsades de pointes or ventricular fibrillation). In more mild cases, the classical electrocardiogram findings are flattened or inverted T-waves and the presence of large U-waves.

Singh et al. review the clinical patterns and biochemical features of the different etiologies of hypokalemia-related neuromuscular weakness. They discuss how this can present with hyporeflexia, tetany, and paralysis. They recommend correction of this electrolyte abnormality.

Figure/Illustration A is an ECG that demonstrates inverted T-waves and large U-waves (red circle). This finding is classically seen in patients with hypokalemia.

Incorrect Answers:
Answer 1: Elevated creatinine is a finding that can be seen in patients suffering from acute kidney injury. In young, healthy individuals, BUN may also be increased out of proportion to creatinine, with a BUN:Cr ratio of > 20. In this patient, who has been hydrating with water during the marathon, pre-renal injury is less likely than electrolyte abnormalities.

Answer 2: Hypercalcemia results in characteristic symptoms of “bones, stones, abdominal groans, and psychiatric overtones,” reflecting bone pain, kidney stones, abdominal pain/cramping, and alteration in mental status. This patient does not have any of these symptoms and complains of muscle pain over bone pain.

Answer 3: Hypermagnesemia can result in weakness and decreased reflexes, but also presents with confusion and decreased respiratory rate. Risk factors for the development of this condition include use of magnesium cathartics, antacids, laxatives, or dietary supplements.

Answer 5: Uremia is common in patients with chronic kidney disease, and mild uremia may be present in patients suffering from pre-renal acute kidney injury. These patients will present with confusion/change in mental status, nausea, vomiting, uremic pericarditis, and a bleeding diathesis due to platelet dysfunction.

Bullet Summary:
Symptomatic hypokalemia presents with weakness, electrocardiogram abnormalities (flat T-waves and U-waves), fatigue, and muscle cramps.