Factitious Total Triiodothyronine(T3) Elevation in a Euthyroid Patient With Paraproteinemia

Background: We report a rare case of a patient treated with levothyroxine for hypothyroidism who also had paraproteinemia and was found to have a clinically inconsistent elevation of T3 by RIA. Clinical Case: A 72 Year old African American female with a history of hypothyroidism and IgG kappa Multiple Myeloma (MM) was admitted to the hospital for altered mental status. Her hypothyroidism had been well controlled for years on a stable dose of levothyroxine 0.075mg daily. Review of systems were negative pertinent to thyroid dysfunction. Family history: negative for thyroid disease. On physical exam, an elderly female clinically euthyroid without palpable thyromegaly but was confused and disoriented. Initial Vital signs: BP 117/67, HR 62, RR 14, T 98, SpO2 99% on room air. BMI 19. EKG: normal sinus rhythm, CXR: normal, TSH: 6.27 (0.55-4.78 uIU/mL), total T3: >600 (60-181ng/dL), total T4: 4.5 (3.2-12.6 ug/dL), FT4: 1.22 (0.89-1.76 ng/dL), hemoglobin: 6.6 (12-16 g/dL), hematocrit: 20.9 (38-47 %), Na: 132 (136-145 mmol/L), K: 4.0 (3.5-5.1 mmol/L), Cl: 104 (98-10/ mmol/L), BUN: 45 (20-31 mmol/L), creatinine: 2.8 (0.6-1.0 mg/dL), total protein: 10.1 (5.7-8.2 g/dL), albumin: 1.8 (3.4- 5.0 g/dL), A:G ratio: 0.22 (0.60-1.50 mmol/L). Serum protein electrophoresis revealed Gamma Globulin 5.8 (0.8-1.7 g/dL), Kappa 9270 mg/L (3.3 -19.4 mg/L) Lambda 9.3 (5.7-26.3mg/L), K/L 996.7 (0.26 -1.65), B2 - macroglobulin: 17.9 (ref: <or= 2.51mg/L) which is consistent with an M- spike migrating in the gamma globulin region. Serum TPO, TG, TSI antibodies were negative. Further testing again reported Total T3 >600 with normal reverse T3 21(8-25 ng/dL). Conclusion: Rare cases of factitious elevations of thyroid hormone have been reported in patients with elevated abnormal IgG or IgA proteins having high binding affinity for thyroid hormone.([1]) This hypothyroid patient was clinically and biochemically euthyroid except for a dramatic but clinically inconsistent elevated total T3. She also had multiple myeloma with paraproteinemia (IgG Kappa M spike). The few cases reported to date have shown factitious elevation of either or both total T4 and total T3. In our case the factitious elevation was limited to total T3. We alert clinicians to be aware of factitious elevation of thyroid hormones due to high affinity binding to immunoglobulins. In our case this caused spurious elevation of total T3, but not total T4, in a patient with multiple myeloma and an IgG kappa M spike paraprotein. Reference: 1: Marianna Antonopoulou, Arnold Silverberg, “Spurious T3 Thyrotoxicosis Unmasking Multiple Myeloma”, Case Reports in Endocrinology, vol. 2013, Article ID 739302, 3 pages, 2013. https://doi.org/10.1155/2013/739302