Summary: We report a case of a 59-year-old woman with Cushing's disease who developed hyperthyroidism following treatment of hypercortisolaemia. The patient with a history of recurrent hospitalisations caused by multi-sited soft tissue abscesses was admitted with sepsis. Both her medical history and physical examination suggested Cushing's syndrome. The initial hormonal diagnostic process, conducted after sepsis treatment, brought forth conflicting results. However, hormonal assessment repeated 3 months later indicated pituitary hypercortisolaemia, which was confirmed through bilateral inferior petrosal sinus sampling and was successfully treated with transsphenoidal pituitary surgery. Three months after the surgery, the patient was readmitted to our epartment with symptoms of hyperthyroidism, which was confirmed by laboratory tests. Thyroid scintiscans indicated Graves' disease. However, the absence of anti-thyroid stimulating hormone antibodies suggested other etiologies of hyperthyroidism. Eventually, the patient underwent radioiodine therapy. Currently, her condition is improving and she has had no recurrence of abscesses, severe infections, or hyperthyroidism. In conclusion, while clinical manifestation of hypercortisolaemia might be non-specific, its treatment may trigger the development of autoimmune diseases.
Learning points: The presence of recurrent severe infections should prompt physicians to consider the possibility of hypercortisolaemia. Chronic hypercortisolism is debilitating and can lead to significant disability. Dexamethasone suppression testing in patients with active or recent severe inflammatory or infectious illnesses may produce misleading or confusing results. Clinicians should be aware of the potential development of autoimmune diseases following successful treatment of hypercortisolaemia.