[Hyperammonemia during hypothyroidism: an unusual biohumoral finding normalized by hormonal replacement treatment]

In this paper we describe 3 clinical cases of hypothyroidism causing myopathy and hyperammonemia. The patients, all females, aged 32 to 64 years, presented with hoarseness, fatigue, dyspepsia (case I), difficulty speaking secondary to the sensation of tongue swelling and hoarseness (case II), and progressive weight gain and difficulty speaking secondary to tongue swelling after delivery (case III). Laboratory tests showed a marked increase in creatine phosphokinase (up to 4090 U/L; normal values 24-176 U/L) of muscle origin, and an increase in transaminases and ammonia (124 to 150 micrograms/dL; normal values up to 75 micrograms/dL). Hypothyroidism was confirmed by TSH > 100 microIU/mL (normal values 0.3-5 microIU/mL). Treatment only with L-thyroxine determined the complete and persistent recovery of well-being and of biochemical abnormalities. The patients remained in good health after more than 2 years of follow-up. Our finding of hyperammonemia caused by the lack of thyroid hormones in 3 patients with hypothyroid myopathy appears to be of a certain interest as, to our knowledge, this phenomenon has not been previously described. In conclusion our hypothesis is that increased muscle production of ammonia secondary to the hypothyroid myopathy determined an increased ammonia load, resulting in hyperammonemia. Decreased liver ureagenesis induced by the lack of thyroid hormones also contributed to the hyperammonemia.