Common causes of acquired hypothyroidism in a 12‑year‑old girl
Chronic autoimmune lymphocytic thyroiditis / Hashimoto disease
- most common;
- often progressive,
- associated with anti‑TPO/anti‑TG and other autoimmune endocrinopathies.
Iatrogenic
- total/subtotal thyroidectomy;
- radioactive iodine ablation;
- external neck irradiation (cancer, Hodgkin lymphoma).
- lithium,
- amiodarone,
- interferon,
- immune checkpoint inhibitors,
- excessive iodine (contrast, topical antiseptics),
- iodine deficiency in endemic areas.
Central hypothyroidism
- pituitary or hypothalamic disease (tumour, surgery, radiation, trauma, lymphocytic hypophysitis) causing low/normal TSH with low free T4.
Post‑infectious or subacute/painless thyroiditis
- destructive thyroiditis may follow viral illness and evolve to permanent hypothyroidism in some.
Infiltrative and systemic disease
- sarcoidosis
- haemochromatosis
- Riedel thyroiditis (rare in children).
Late manifestation of congenital defects or dyshormonogenesis
- previously compensated congenital cases presenting later in childhood or adolescence.
Rare genetic/autoimmune polyglandular syndromes
- APS type 1/2 association in children with other autoimmune endocrinopathies.
Clinical manifestations brief discussion
Growth and pubertal effects
- reduced growth velocity
- delayed bone age
- potential loss of height potential if prolonged untreated
- delayed or arrested puberty and menstrual irregularities in adolescents.
- decreased concentration
- slowed processing speed
- fatigue
- behavioral change and worsening scholastic performance
- subtle cognitive deficits even in subclinical disease.
General systemic features
- constitutional tiredness
- cold intolerance
- weight gain with poor linear growth
- constipation
- dry coarse skin
- brittle hair
- facial puffiness
- periorbital oedema.
- bradycardia, diastolic hypertension,
- reduced exercise tolerance
- reversible dyslipidaemia (elevated LDL)
- potential pericardial effusion in severe cases.
Neuromuscular signs
- slowed deep tendon reflex relaxation
- proximal muscle weakness
- myalgias
- rarely neuropathy.
Thyroid examination and red flags
- diffuse firm painless goitre typical of autoimmune disease
- nodularity or rapidly enlarging painless mass raises concern for lymphoma or carcinoma — urgent FNA and haematology referral.
Associated autoimmune features
- symptoms/signs of type 1 diabetes, celiac disease, adrenal insufficiency, vitiligo — screen guided by history/family history.
Clinical severity spectrum
- from asymptomatic/subclinical biochemical abnormalities to overt hypothyroidism with growth and neurocognitive compromise.
Laboratory findings brief discussion
Thyroid function tests
- Primary acquired hypothyroidism: ↑TSH with ↓free T4 (overt) or ↑TSH with normal fT4 (subclinical).
- Central hypothyroidism: low/( TSH with ↓free T4; assess other pituitary axes.
Autoantibodies and supportive serology
- Anti‑TPO positive in majority of autoimmune cases; titre correlates with risk of progression
- Anti‑TG may be positive; TSH‑receptor antibodies only if clinical thyrotoxicosis or maternal transfer suspected.
Imaging and tissue diagnosis
- High‑resolution neck ultrasound: diffuse hypoechogenicity, heterogeneity, micronodularity in autoimmune thyroiditis; identify nodules for FNA.
- FNA cytology for suspicious nodules; in rapidly enlarging mass perform cytology plus flow cytometry/immunophenotyping to exclude primary thyroid lymphoma.
Ancillary laboratory abnormalities
- Dyslipidaemia: elevated LDL and total cholesterol.
- Haematologic: normocytic anaemia or macrocytosis occasionally.
- Hyponatraemia and hypoglycaemia in severe, prolonged hypothyroidism or when concomitant adrenal insufficiency present.
- Pituitary workup when central pattern
- Morning cortisol, ACTH stimulation if indicated, GH axis testing, pituitary MRI to identify structural causes before or during endocrine therapy.