Problem 1: Diagnosing the Endocrine Disorder

Clinical scenario: A 35-year-old patient visits the doctor. Lab results: TSH = 15 mIU/L (high), T4 = 2 µg/dL (low, normal = 5–12). He complains of fatigue, weight gain, cold intolerance, constipation, and a puffy face.

Step-by-step reasoning:

Step 1 — Interpret TSH: TSH is high. In the HPT axis, high TSH means the pituitary is "shouting" at the thyroid. This occurs when T4 is low (less negative feedback → TSH rises compensatorily).

Step 2 — Interpret T4: T4 is low. Confirms inadequate thyroid hormone production. Low T4 = hypothyroidism.

Step 3 — Determine primary vs secondary: In secondary hypothyroidism (pituitary failure), TSH would be LOW (pituitary can't make TSH). Here TSH is HIGH → the thyroid is the problem (primary hypothyroidism). The pituitary is intact and compensating.

Step 4 — Match symptoms: Fatigue, weight gain, cold intolerance, constipation, puffy face = classic myxoedema (adult hypothyroidism). Low T4 → low BMR → all these features.

Step 5 — Diagnosis: Primary hypothyroidism (myxoedema) in an adult.

Step 6 — Treatment: Oral levothyroxine (T4 replacement). Being a steroid/amino acid derivative (lipid-soluble), T4 is absorbed orally. TSH would be used to monitor treatment response (target: TSH normalisation).