THYROID GLAND LEC 4

HYPOTHYROIDISM
Hypothyroidism
Decreased thyroid hormone levels
Low T4
Possibly Low T3 too.
Raised TSH (unless pituitary problem!)

Classification of hypothyroidism
Autoimmune thyroiditis (chronic lymphocytic thyroiditis)
Non-goitrous: primary myxoedema
Goitrous: Hashimoto’s disease
Iatrogenic
After thyroidectomy
After radioiodine therapy
Drug induced (anti-thyroid drugs, para-aminosalicylic acid and
Iodides in excess)
Dyshormonogenesis
Goitrogens
Secondary to pituitary or hypothalamic disease
Thyroid agenesis
Endemic cretinism :Often goitrous and due to iodine deficiency

Cretinism (fetal or infantile hypothyroidism)
Cretinism is the consequence of inadequate thyroid hormone production during fetal and neonatal development. ‘Endemic cretinism’ is due to dietary iodine deficiency, whereas sporadic cases are due to either an inborn error of thyroid metabolism or complete or partial agenesis of the gland.
A hoarse cry, macroglossia and umbilical hernia in a neonate with features of thyroid failure suggest the diagnosis. Immediate diagnosis and treatment with thyroxine within a few days of birth are essential to prevent damage in utero progressing and if physical and mental development are to be normal.
Biochemical screening of neonates for hypothyroidism using TSH and T4 assays on a heel prick blood sample is widespread.
Women taking anti-thyroid drugs may give birth to a hypothyroid infant and radioactive iodine must never be given to pregnant women.

Adult hypothyroidism
The term myxoedema should be reserved for severe thyroid failure and not applied to the much commoner mild thyroid deficiency.
Thyroid function tests: These show low T4 and T3 levels with a high TSH (except in the rare event of pituitary failure) .
High serum levels of TPO antibodies are characteristic of autoimmune disease.
Treatment
Oral thyroxine (0.10–0.20 mg) as a single daily dose is curative.
Caution is required in the elderly or those with cardiac disease; in such cases the replacement dose is commenced at 0.05 mg daily and increased cautiously.
If a rapid response is required, triiodothyronine (20 ?g t.d.s.) may be used.

Myxoedema
The signs and symptoms of hypothyroidism are accentuated. The facial appearance is typical; there is often supraclavicular puffiness, a malar flush and a yellow tinge to the skin.
Myxoedema coma, characterised by altered mental state, hypothermia and a precipitating medical condition, for example cardiac failure or infection, carries a high mortality rate.
Treatment comprises thyroid replacement.
If the body temperature is less than 30?C the patient must be warmed slowly.
Intravenous broad-spectrum antibiotics and hydrocortisone (in divided doses) are recommended.

Dyshormonogenesis
Genetic deficiencies in the enzymes controlling the synthesis of thyroid hormones account for a minority of cases of neonatal hypothyroidism and goitre.
These are usually inherited in an autosomal recessive pattern and a family history is common.
The most common abnormalities affect TPO activity and thyroglobulin synthesis.
A classic example of dyshormonogenesis due to TPO deficiency is Pendred’s syndrome, in which goitre is associated with severe sensorineural hearing impairment and abnormality of the bony labyrinth observed on CT examination of the temporal bones.


THYROIDITIS
Chronic lymphocytic (autoimmune) thyroiditis (Hashimoto’s disease) ;
This common condition is usually associated with raised titres of thyroid antibodies.
Females > Males
Runs in Families.
It commonly presents as a goitre, which may be diffuse or nodular with established or subclinical thyroid failure.
Primary myxoedema without detectable thyroid enlargement represents the end-stage of the pathological process.
Clinical features
The onset may be insidious and asymptomatic or so sudden and painful that it resembles the acute form of granulomatous thyroiditis.
Mild hyperthyroidism may be present initially, but hypothyroidism is inevitable and may develop rapidly or extremely slowly.
Papillary carcinoma and malignant lymphoma are occasionally associated with autoimmune thyroiditis.
Diagnosis
Biochemical tests of thyroid function are of diagnostic value only if hypothyroidism is present.
Significantly, raised serum levels of one or more thyroid antibodies are present in over 85% of cases.
Nevertheless, differential diagnosis from nodular goitre, carcinoma and malignant lymphoma of the thyroid is not always easy.
FNAC is the most appropriate investigation although abundant lymphocytes may make the cytological distinction between autoimmune thyroiditis and lymphoma difficult. When there is doubt about neoplastic disease, which may coexist with thyroiditis, diagnostic lobectomy may be necessary.

Treatment
Full replacement dosage of thyroxine should be given for hypothyroidism and if the goitre is large or symptomatic because some (under TSH stimulation) may subside with hormone therapy.
More minor manifestations of the condition, do not justify thyroxine replacement if thyroid function is biochemically normal; however, long-term surveillance is necessary because of the risk of late thyroid failure.
Occasionally, the goitre increases in size despite hormone treatment and, in these circumstances, there may be a favourable response to steroid therapy.
Thyroidectomy may be necessary if the goitre is large and causes discomfort.
An increase in size of a longstanding lymphocytic goitre should be assessed urgently because of the possibility of the development of malignant lymphoma.

Subacute (de Quervain’s) Thyroiditis ;
Preceding viral infection
Infiltration of the gland with granulomas
Painful goitre
Hyperthyroid phase à Hypothyroid phase
There is a raised erythrocyte sedimentation rate and absent thyroid antibodies, the serum T4 is high normal or slightly raised and the 123I uptake of the gland is low.
The condition is self-limiting and after a few months the goitre subsides.
If diagnosis is in doubt it may be confirmed by FNAC, radioactive iodine uptake and a rapid symptomatic response to prednisone.
The specific treatment for the acute case with severe pain is to give prednisone.
If thyroid failure is prominent, treatment with thyroxine may be required until function recovers.

Riedel’s thyroiditis
Riedel’s thyroiditis is very rare, accounting for 0.5% of goitres. Thyroid tissue is replaced by cellular fibrous tissue, which infiltrates through the capsule into muscles and adjacent structures, including the parathyroids, recurrent nerves and carotid sheath.
It may occur in association with retroperitoneal and mediastinal fibrosis and is most probably a collagen disease.
The goitre may be unilateral or bilateral and is very hard and fixed.
The differential diagnosis from anaplastic carcinoma can be made with certainty only by biopsy, when a wedge of the isthmus should also be removed to free the trachea.
Treatment is with high-dose steroids and thyroxine replacement.
A reduction in the size of the goitre and long-term improvement in symptoms are to be expected if treatment is commenced early.