Thyroiditis
Chronic
Iymphocytic (autoimmune) thyroiditis
This common condition is usually associated
with raised titres of thyroid antibodies. Not infrequently there is a family
history of other autoimmune disease. It commonly presents as a multinodular
goitre with established or subclinical thyroid failure, although it may present
as a discrete swelling. Features of chronic lymphocytic (focal) thyroiditis are
commonly present on histological examination in association with other thyroid
disease — notably toxic goitre. Primary myxoedema without detectable thyroid
enlargement represents the end stage of the pathological process.
Clinical
features
As might be expected from the varied
histological picture (above), the onset, the thyroid status and the type of
goitre vary profoundly from case to case. 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. The goitre is usually lobulated, and
may be diffuse or localised to one lobe. It may be large or small, and soft,
rubbery or firm in consistency — depending upon the cellularity and the
degree of fibrosis. The disease is commonest in women at the menopause, but may
occur at any age. Papillary carcinoma and malignant lymphoma are occasionally
associated with autoimmune thyroiditis.
Diagnosis
Biochemical tests of thyroid function vary
with the thyroid status and are of diagnostic value only if hypothyroidism is
present. Significantly, raised titres of one or more thyroid antibodies are
present in over 85 per cent 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 (Fig. 44.46). When there is doubt about neoplastic
disease, which may coexist with thyroiditis, operation is 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 such as a small goitre with raised antibody
titres, or histological evidence of thyroiditis in association with other
thyroid disease, 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 spite
of 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. The clinician must, however, be cautious when a
lymphocytic goitre increases in size and becomes unresponsive to thyroxine as
this may be due to the development of malignant lymphoma.
Granulomatous
thyroiditis (subacute thyroiditis —de
Quervain’s thyroiditis)
This is due to a virus infection. (An epidemic
reported from Israel was due to a mumps virus.) In a typical subacute
presentation there is pain in the neck, fever, malaise and a firm, irregular
enlargement of one or
both thyroid lobes. There is a raised
erythrocyte sedimentation rate and absent thyroid antibodies, the serum T4 is
high, normal or slightly raised, and the
123 I
uptake of the gland is
low The condition is self-limiting and in a few months the goitre has subsided;
subsequent hypothyroidism is rare. In 10 per cent of cases the onset is acute,
the goitre very painful and tender, and there may be symptoms of
hyperthyroidism. Thirty-five per cent of cases are asymptomatic but for the
presence of the goitre. If diagnosis is in doubt, it may be confirmed by FNAC,
radioactive iodine uptake and by a rapid symptomatic response to prednisone. The
specific treatment for the acute case with severe pain is to give prednisone
10—20 mg daily for 7 days and the dose is then gradually reduced over the next
month.
Riedel’s
thyroiditis
This is very rare, accounting for 0.5
per cent of goitres. Thyroid tissue is replaced by cellular fibrous tissue
which infiltrates through the capsule into adjacent muscles, paratracheal
connective tissue and the carotid sheaths. 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 only be made with
certainty by biopsy, when a wedge of the isthmus should also be removed to free
the trachea. If unilateral, the other lobe is usually involved later and
subsequent hypothyroidism is common.