Klinisch redeneren: diagnostiek bij thyreotoxicose in de eerste lijn: een case-report

Clinical reasoning: diagnosis of thyrotoxicosis in family medicine: a case report. Case report: A 15-year-old girl consulted her family doctor because of general malaise, fatigue and hair loss. A blood test was performed for further diagnosis. It showed an iron deficiency anaemia and undetectable TSH. While iron deficiency was being substituted, further investigation regarding thyrotoxicosis was performed. Differential diagnosis: FT4 and FT3 appeared to be truly elevated, while no TSH receptor antibodies were measurable. Further clinical investigation showed us two possible explanations for thyrotoxicosis: silent thyroiditis or antibody-negative Graves' disease. Distinction between these is paramount given their different treatment and prognosis. When calculating the chance of Graves' disease, we aimed for a threshold of 10% to start treatment and/or referral to the endocrinologist. If we took the clinic (via Wayne's index) and biochemistry (TSH, FT4 and TSH receptor antibodies) into account, we arrived at a disease chance of 1% if we started from the waiting room chance of almost 0,1%. Case progression: Scintigraphy could have brought us above the threshold given its strong demonstrative power. However, this was negative, so the diagnosis of silent thyroiditis was made. Biochemistry was followed up several times, whereby the thyroid parameters and iron status normalized. Discussion: Thyroid disorders have very non-specific symptoms and clinical signs, where their individual value has not been sufficiently investigated. Conclusions should not be drawn solely based on the presence or absence of TSH receptor antibodies. A scintigraphy is the gold standard examination when TSH receptor antibodies are negative and does have its place in the diagnosis in selected cases.