Subacute Thyroiditis Revealing a Pheochromocytoma

ABSTRACT Objective: Subacute thyroiditis is an inflammatory thyroid disorder, and its co-existence with pheochromocytoma is uncommon. Both diagnostic entities have similar clinical signs, which can mislead a correct diagnosis. Methods: We report a case of a patient with pheochromocytoma revealed by subacute thyroiditis and describe the clinical course and management. Results: Hyperthyroidism in our patient was characterized by association of elevated erythrocyte sedimentation rate, high serum free thyroxin and free triiodothyronine levels, low thyroid-stimulating hormone, and negativity of circulating thyroperoxidase antibodies and thyrotropin-receptor antibodies, in the presence of low thyroidal technetium uptake. Retrieval of past medical history revealed discovery of a left adrenal mass on ultrasonography performed 2 years prior for occasional hypertension. The catecholamine-induced pro-inflammatory state seems to be the result of the effects of catecholamines on humoral immunity in our patient. The therapeutic challenge concerns management of hyperthyroidism and optimal control of hypertension before surgery for pheochromocytoma. Our patient responded well to glucocorticoids and labetalol characterized by α:β-blocking action. There is no optimal medical strategy, and the choice of the treatment should be based on individualized risks and benefits. Conclusion: Our case underlines the importance of considering interactions among the adrenergic signaling pathways, thyroid hormones, and the immune system in the diagnosis and clinical workup. Abbreviations: α-AR and β-AR = alpha-adrenergic receptor and beta-adrenergic receptor BP = blood pressure FT3 = free triiodothyronine FT4 = free thyroxin TPOAb = thyroperoxydase TRAb = thyrotropin-receptor antibodies TSH = thyroid-stimulating hormone 18F-DOPA PET = 18-fluorodopa positron emission tomography