Free Triiodothyronine Toxicosis in Adolescent Monozygotic Twin Brothers

Free triiodothyronine toxicosis is a rare condition, expressed by isolated triiodothyronine concentration elevation, resulting in an overt hypermetabolic state. Diagnosis and treatment are particularly important in young populations during puberty, with intensive intellectual and physical development. We present a case of monozygotic adolescent male twins, with cardiovascular symptoms, along with anxiety, hypersensitivity and insomnia. The free triiodothyronine toxicosis in the absence of anti-thyroid antibodies. Successful treatment with symptom relief and laboratory results normalization was achieved after 8 weeks of anti-thyroid medication with beta-blocker addition. The described condition may be an early stage of developing disease, so further follow-up is obligatory. Because the case presents an atypical population for the disorder, with brothers additionally being monozygotic twins, genetic factors should be taken into consideration in the event of disease progression.