Purpose

Progressive cognitive disorders are not always caused primarily by neurodegenerative diseases. This case report emphasizes the importance of taking rare metabolic disorders into consideration in the differential diagnosis in patients of all ages. It also shows the possible risk of corticosteroids in the treatment of unexplained neurological symptoms.

Case description

We report on the case of a 60-year-old female who presented mild dementia with progression and fluctuations for the last 5 years, scanning speech and wide-base gait. Due to a significantly elevated level of anti-thyroid peroxidase antibodies, steroid responsive encephalopathy in autoimmune thyroiditis (STREAT) was suspected and steroids were administered. This was a trigger factor for the patient developing coma with severe hyperammonemia. Consequent genetic testing identified a pathogenic variant of the OTC (ornithine transcarbamylase) gene.

Comment

Late-onset ornithine transcarbamylase deficiency can be a rare cause of cognitive impairment. It is reasonable to determine the level of ammonia in patients with non-specific symptoms, as hyperammonemia can cause permanent brain damage.