Case 113

1. Lorena Marcano-Bonilla, MD, Ph.D. and Lori Sokoll, Ph.D.

An adult with a history of relapsing multiple sclerosis and hypertension presents to her follow up appointment complaining of increasing fatigue and difficulty concentrating. Upon further questioning, the patient denies tremors, palpitations, changes in bowel movements, weight loss, changes in vision, or heat intolerance. Among the tests ordered were thyroid function tests. Serum TSH and free T4 (FT4) were 0.03 microIU/mL (reference range: 0.50-4.50 microIU/mL) and 5.2 ng/mL (0.8-1.8 ng/dL), respectively. TSH and free T4 results were within the reference range at visits one and three years prior.

What is the explanation for these results?