What's the most likely clinical diagnosis?

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Hypothyroidism

Describe the physiological regulation of thyroid hormones

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The physiological regulation of thyroid hormones involves a complex feedback loop involving the hypothalamus, pituitary gland, and thyroid gland:
Hypothalamus – TRH: Releases thyrotropin‑releasing hormone (TRH), stimulating the pituitary.
Pituitary – TSH: TRH triggers release of thyroid‑stimulating hormone (TSH), which stimulates the thyroid gland.
Thyroid – T3 & T4: TSH stimulates production and release of thyroxine (T4) and triiodothyronine (T3).
Negative feedback: High levels of T3/T4 inhibit TRH and TSH release, maintaining balance.

What are differences between T3 & T4

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T3 is more biologically active than T4.
T4 has greater protein‑binding capacity than T3.

Talk about Synthesis of T3 & T4

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Iodide ions enter thyroid follicular cells via active pumping.
Iodide is converted to iodine by TPO (thyroid peroxidase).
Iodine combines with tyrosine to form MIT (monoiodotyrosine) and DIT (diiodotyrosine).
MIT + DIT = T3
DIT + DIT = T4

Signs of hypothyroidism

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Weight gain
Memory loss
Cold intolerance
Constipation
Myxoedema
Bradycardia
Muscle weakness
Pretibial oedema
Dry skin

Causes of hypothyroidism
Primary hypothyroidism

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Iatrogenic
-Surgery
-Radioiodine therapy
-Drugs
Autoimmune (Hashimoto’s)
Iodine deficiency
Idiopathic
Genetic defects in thyroid development
Thyroid hormone resistance syndrome (THRB) (rare)
Congenital biosynthetic defect (dyshormonogenetic goitre) (rare)
Transient thyroiditis (De Quervain’s thyroiditis)
Infiltrative (amyloidosis, sarcoidosis)

Secondary hypothyroidism

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Pituitary failure (rare)
Hypothalamic failure (rare)

If hypothyroidism is due to hypopituitarism, how could TFT differ?

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This will be secondary hypothyroidism:
Low TSH
Low T3 and T4

From the FBC findings given, explain the cause

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Patient has macrocytic anaemia due to antibodies directed against parietal cells, which are responsible for secretion of intrinsic factor that helps in absorption of vitamin B12.
I.e. autoimmune hypothyroidism associated with pernicious anaemia.

She was put on medical therapy; she is not compliant. Which teams should be involved?

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Endocrinologist
Her GP
Family members

Problems associated with emergency surgery in hypothyroid patients

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Pre‑operative
Anaemia
Increased risk of ischaemic heart disease
Increased sensitivity to medications, anaesthetic drugs, and narcotics
Intra‑operative
Airway compromise
Coagulopathy
Post‑operative
Myxoedema coma
Delayed recovery
Poor wound healing

How to improve compliance with thyroid replacement therapy

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Discuss with the patient the reason for non‑compliance
Communication with GP and family members
Medical follow‑up
Simple regimen: single dose in the early morning