Endocrine Abstracts

Introduction: Periodic paralysis is a rare condition characterized by muscle weakness in the presence of triggers including cold, heat, high carbohydrate meals or physical activity. It is classically described in the presence of profound hypokalaemia; when this occurs in conjunction with thyrotoxicosis it is termed thyrotoxic periodic paralysis.

Case history: A 30-year old Nigerian man presented with a 3 h history of inability to move, on a background of recurrent similar episodes over the preceding 2 years. He had associated severe muscle cramps in his upper and lower limbs. On examination he had a profound proximal myopathy. He had a moderately and diffusely enlarged goitre with a loud bruit. There was no retrosternal extension, palpable nodules or neck lymphadenopathy. He had a sinus tachycardia and was tremulous.

Biochemistry: Serum potassium 2.0 mmol/l (3.5–5.5), TSH<0.01 mU/l (0.35–5.5), fT4 72.7 pmol/l (10.0–22.7), CK 2047 u/l (<170). Subsequently TSH-receptor antibodies were found to be elevated at 28.17 U/l (0–0.4).

Treatment: He was treated with intravenous potassium replacement with rapid resolution of his paralysis. He was commenced on Propranolol and Carbimazole as treatment for his thyrotoxicosis. On discharge his potassium was 5.0 mmol/l without additional supplementation. He is now euthyroid, and has had no further episodes of paralysis.

Discussion: Thyrotoxic periodic paralysis (TPP) is a rare complication of hyperthyroidism which is predominantly seen in Asian patients. It is likely due to increased sodium–potassium adenosine triphosphate pump activity (NaK-ATPase), with rapid intracellular shift of potassium into muscles. This may be due to the direct effects of excess thyroid hormone, or indirectly due to sympathetic overactivity. This case provides a rare example of TPP in an Afro-Carribean male and demonstrates the need to consider the diagnosis in any patients presenting with hypokalaemia and weakness.