Spurious t3 thyrotoxicosis unmasking multiple myeloma

Area of Science:

• Endocrinology
• Hematology
• Clinical Chemistry

Background:

• Thyroid function tests are crucial for diagnosing thyroid disorders.
• Elevated triiodothyronine (T3) levels typically indicate hyperthyroidism.
• Spurious laboratory results can arise from various interfering substances.

Purpose of the Study:

• To document a unique case of spurious T3 thyrotoxicosis.
• To investigate the cause of euthyroid hyper-triiodothyroninemia in a patient with normal thyroid status.
• To identify a novel mechanism of laboratory assay interference.

Main Methods:

• Diagnostic evaluation of a 54-year-old woman with incidentally high total T3 levels.
• Thyroid function tests including TSH, T4, and T3.
• Investigation for interfering factors, including thyroid binding globulin abnormalities.
• Diagnosis of multiple myeloma through additional laboratory studies.

Main Results:

• The patient presented with clinically euthyroid status despite a total T3 level exceeding 800 ng/dL.
• Thyroid Stimulating Hormone (TSH) and Thyroxine (T4) levels were within the normal range.
• Subsequent investigations confirmed multiple myeloma, revealing monoclonal gammopathy.

Conclusions:

• Monoclonal immunoglobulins associated with multiple myeloma can interfere with thyroid hormone assays.
• This case identifies a new cause of spurious hyper-triiodothyroninemia due to T3 binding to monoclonal immunoglobulins.
• The findings suggest that certain monoclonal immunoglobulins may specifically bind to T3, leading to diagnostic discrepancies.