Hypokalemic Periodic Paralysis

A 38-year-old man presents to the emergency room for acute onset weakness for the past day.

History. The patient reported acute onset lower extremity weakness that started the same morning of presentation. He felt his proximal muscle weakness was worse in both of his thighs. He attempted to walk but the weakness was so profound that he fell down a flight of stairs in his home. Upon trying to get up, he was unable to move or feel his legs. He also reported that he tried to push himself up and was completely unable to, which prompted him to notice his arms felt profoundly weak.

The patient went on a recent trip to Cuba and upon return 1 month ago noted 1-2 days of watery, non-bloody diarrhea that has since resolved. The patient had a personal history of bipolar II disorder, panic disorder, and hypertension. His list of daily medications included lamotrigine 100 mg, duloxetine 40 mg, and propranolol 80 mg. The patient denies taking any additional over-the-counter medications. He has no known family history of periodic paralysis. However, he does note estrangement with members of his family.

On physical examination, vital signs were unremarkable. The results of the Medical Research Council Manual Muscle Testing scale was 2/5 hip flexion, dorsiflexion, plantar flexion, and knee flexion/extension bilaterally; 2/5 shoulder abduction, elbow flexion, and extension bilaterally; and diffusely decreased reflexes (0/4). General examination, cardiac examination, and pulmonary examination were unremarkable.

Diagnostic testing. Initial laboratory testing showed marked hypokalemia of 1.1 mmol/L pH. Random blood glucose, serum bicarbonate, other electrolytes, and renal and liver function tests were all within normal limits. Thyroid function including thyroid stimulating hormone, free thyroxine (T4), and free triiodothyronine (T3) were also within normal limits. A polymerase-chain reaction test was positive for rhinovirus and enterovirus. An electrocardiogram (EKG) revealed sinus rhythm within normal limits but was significant for U wave (Figure 1). These findings are consistent with hypokalemia.