Question

A $54$-year-old woman is evaluated in the ambulatory care clinic for progressive lethargy and generalized weakness over the past six months. She states she feels persistently cold even during warm weather and has been struggling with constipation. Over the same period, she has been involved in several minor motor vehicle collisions, which she attributes to "not seeing cars coming from the side." Physical examination reveals pale, dry skin, puffiness around the eyes, and a delayed relaxation phase of the deep tendon reflexes. Confrontational visual field testing demonstrates decreased peripheral vision bilaterally.

Laboratory studies reveal:
Hemoglobin: $11.2$ g/dL
Thyroid-stimulating hormone (TSH): $1.8$ $\mu$ U/mL (Normal: $0.4$-$4.0$ $\mu$ U/mL)
Free thyroxine (T4): $0.5$ ng/dL (Normal: $0.9$-$1.7$ ng/dL)

Which of the following is the most likely underlying mechanism for this patient's laboratory findings?