Thyrotoxic Periodic Paralysis in an Active Duty Soldier

Introduction : Thyrotoxic periodic paralysis (TPP) is a rare and life threatening presentation of thyrotoxicosis. Typically, patients present with severe hypokalemia, muscle weakness, and hyperthyroidism. It is reversible with judicious potassium replacement and antithyroid medication. Given the risk of cardiac arrhythmia and respiratory arrest, TPP is an important diagnosis to consider in the setting of thyrotoxicosis.

Case Description : A 24 year old Army active duty male presented to the emergency department with one day of ascending lower extremity weakness. He has had five years of intermittent episodes of lower extremity paresthesia, usually lasting several hours. He also has a history of mild palpitations. He otherwise denied nausea, vomiting, diarrhea, weight loss or vision changes. He denied any family history of thyroid disease, electrolyte abnormalities or neurological disease. He denied use of alcohol, tobacco or recreational drugs. On examination, vital signs showed a heart rate of 103 beats/minute, blood pressure of 144/74 mm Hg, respiratory rate of 20, and oxygen saturation of 96% on room air. Head and neck exam did not reveal exophthalmos, lid lag or thyromegaly. His cardiac exam demonstrated tachycardia with normal rhythm without murmurs. His neurologic exam showed 4/5 strength at the hip flexors bilaterally, but otherwise normal deep tendon reflexes and sensation throughout. He did not have a tremor or cerebellar signs.  Cranial nerves and respiratory muscles were intact. Laboratory evaluation including hemoglobin, renal function, sodium, calcium and glucose were within normal limits. Serum potassium was 1.9 mEq/L and magnesium 1.4 mEq/L. Thyroid function tests showed a free T4 of 2.01 ng/dL (normal 0.7-1.48) and TSH was < 0.01 mcIU/mL (normal 0.35-4.94). He was managed with intravenous fluids, and potassium chloride and magnesium sulfate replacement. His symptoms resolved with normalization of his electrolytes overnight. Endocrinology recommended initiation of methimazole 5 mg daily with plans for outpatient evaluation for etiology of thyrotoxicosis.

Discussion : TPP is an acquired case of hypokalemic periodic paralysis. TPP is characterized by abrupt onset of hypokalemia and paralysis/paresis. It is thought to be caused by sensitization of the sodium/potassium ATP-ase on skeletal muscle by excess thyroid hormone leading to intracellular shift of potassium. It can be associated with any etiology of thyrotoxicosis. TPP is a life threatening entity to consider in patients who present with hypokalemic paralysis, as the mainstay of treatment and prevention of recurrence is antithyroid therapy.