23rd May 2025

Hashimoto’s disease

• Hashimoto’s’ thyroiditis (also known as chronic autoimmune of atrophic thyroiditis) is the commonest form of hypothyroidism in non-iodine deficient areas. Its peak incidence is mainly between 30–50-year-olds with female predominance. 
• It is an autoimmune disease associated with HLA-DR5 genotype. Cytotoxic T cells attack the follicular cells of the gland and associated with unregulated production of autoantibodies against thyroid peroxidase (TPO), and thyroglobulin(Tg).  As a result, the gland is destroyed and hypofunction results.

Clinical picture

• It can be either subclinical (75%) or with overt clinical picture of hypothyroidism (20%) (see full description above). It is of insidious onset slowly progressing over months to years. 
• In the early stage, patients occasionally may have painless goitre especially which tends to be rubbery and of symmetrical enlargement. Hashitoxicosis (5%) sometimes present with transient hyperthyroidism picture. Upon later stage (end-stage gland extensive fibrosis), the gland tends to be of normal size as seen in  atrophic thyroiditis. Hypothyroidism picture is predominant. Patients have increased risk to other autoimmune conditions as T1DM, SLE, Grave’s disease, Addison disease, other HLA-associated conditions, or non-Hodgkin lymphoma.  

Investigations

• TFTs: within the early-stage transient hyperthyroidism picture occurs then progress to hypothyroid picture of high TSH and low levels of T3 and T4.
• Thyroid antibodies: may be positive for anti-TPO (>90%) also known as thyroid microsomal antibodies, and anti-Tg (20-25%).
• Other blood tests can show macrocytic anaemia and hypercholesterolemia.
• Thyroid biopsy: It is characterised with extensive infiltration of the thyroid parenchyma by lymphocytes and plasma cells. Germinal centres are formed as a result. Occasionally done in case of malignancy suspicion.

Prognosis and management

• The long-term prognosis of the chronic type is good because it can be easily corrected with T4 replacement. Local manifestations due to goitre size are not common. However, in case of rapidly enlarging goitre and pain, further investigation may be required. A short course of prednisolone may prove helpful. 
• The mainstay of management for hypothyroidism is oral thyroxine replacement.
• Levothyroxine has a long half-life which enables the patient to take 2 doses at once if a dose is omitted. Normal metabolic state should be restored gradually to avoid precipitating cardiac arrhythmias. Fasting ingestion of levothyroxine in the morning or the evening is recommended, as concurrent ingestion of calcium, iron, food, and other medications may impair its absorption. NICE guidelines advise the following:
  • For adults <65 with primary hypothyroidism and no cardiovascular disease history, start levothyroxine at a dosage of 1.6 mcg/kg of body weight per day (rounded to the nearest 25 mcg).
  • Adults ≥ 65 and patients with cardiovascular history, start levothyroxine at a dose of 25 to 50 mcg/ day with titration by 25 mcg at 4-week intervals until normal metabolic state and TSH level is reached.
  • In antenatal and perinatal period: Patients who become pregnant and on replacement therapy, recommendation to increase levothyroxine by 25 mcg. Dose requirements can increase by 25-50% in pregnancy due to increased thyroid-binding globulin (TBG), to avoid impaired cognitive function in offspring.