Thyroid Disorders

INTRODUCTION

Thyroid disorders can be a diagnostic trap in family practice. Thyroid function tests are the basis of diagnosis. The serum TSH, the most sensitive index of thyroid function, is the key test. Various thyroid antibodies aid specific diagnosis. Relative values are summarised in Table T4.

HYPOTHYROIDISM (MYXOEDEMA)

• Typically physical and mental slowing, lethargy, constipation, cold intolerance and characteristic signs (e.g. dry, cool skin)

• T₄—subnormal, TSH elevated (>10 is clear failure)

• TSH ↑; T₄ N → subclinical hypothyroidism ?treat

Thyroid medication Thyroxine 100–150 mcg daily (once daily)

Note: Start with low doses (25–50 mcg/d) in elderly and ischaemic heart disease.

Monitor TSH levels monthly at first, then 2–3 mthly and when stable on optimum dose of T₄, every 2–3 yrs.

HASHIMOTO THYROIDITIS (AUTOIMMUNE THYROIDITIS)

Commonly presents as postpartum hypothyroidism (thyroiditis):

• bilateral goitre, firm and rubbery

• may be hypothyroid or euthyroid (possible thyrotoxic early)

Diagnosis confirmed by a strongly +ve anti-thyroid antibody titre and/or fine-needle aspiration cytology.

NEONATAL HYPOTHYROIDISM

This demands early diagnosis by neonatal screening to avoid intellectual disability (cretinism): thyroxine replacement should be started by the 14th day.

HYPERTHYROIDISM (THYROTOXICOSIS)

Classic symptoms of hyperactive metabolism, incl. heat intolerance, agitation, restlessness, warm and sweaty hands, may be absent in elderly patients. Avoid dismissing it as anxiety.

• T₃ (and T₄) elevated, TSH suppressed

• Possible anti-thyroid peroxidase antibodies (TPO Ab)

• Radioisotope scan a very useful test

Refer to endocrinologist for treatment.

SUBACUTE THYROIDITIS

Usually transient and often follows a viral-type illness. May be pain over goitre and fever.