Portal-systemic encephalopathy and hypothalamic hypothyroidism: effect of thyroid hormone on ammonia metabolism

We describe a 53-year-old woman with portal-systemic encephalopathy and altered thyroid function. Endocrinological studies revealed low levels of free thyroid hormone with an inappropriately low level of thyroid-stimulating hormone that responded to bolus injection of thyrotropin-releasing hormone with a normal but somewhat delayed pattern. On the diagnosis of hypothalamic hypothyroidism, she was treated with levothyroxine sodium. Thyroid hormone replacement improved not only the symptoms of hypothyroidism but the hyperammonemia and consciousness disturbance, which suggested a hitherto undescribed possibility that hypothyroidism may be an exacerbation factor of hyperammonemia and portal-systemic encephalopathy.