It would indeed be rash for a mere pathologist to venture forth on the uncharted sea of the endocrines, strewn as it is with the wrecks of shattered hypotheses, where even the most wary mariner may easily lose his way as he seeks to steer his bark amid the glandular temptations whose siren voices have proved the downfall of many who have gone before. William Boyd (1885–1969)
Thyroid disorders can be a diagnostic trap in family practice and early diagnosis is a real challenge. A family practice of 2500 patients can expect one new case of thyroid disorder each year and 10 ‘cases’ in the practice.1 The diagnosis of an overactive or underactive thyroid can be difficult as the early clinical deviations from normality can be subtle.
The clinical diagnosis of classical Graves disease is usually obvious with the features of exophthalmos, hyperkinesis and a large goitre but if the eye and neck signs are absent it can be misdiagnosed as an anxiety state. Elderly patients may present with only cardiovascular signs, such as atrial fibrillation and tachycardia, or with unexplained weight loss.
The hypothyroid patient can be very difficult to diagnose in the early stages, especially if the patient is being seen frequently. Hypothyroidism often has a gradual onset with general symptoms such as constipation and lethargy.
If suspected, serum thyroid stimulating hormone (TSH) or thyrotropin should be requested.
Other common endocrine disorders include diabetes mellitus, hyperprolactinaemia, calcium metabolic disorder, PCOS, sexual dysfunction and subclinical hypogonadism. They may be difficult to diagnose in the early stages of development. The pituitary is the master gland and its regulating hormones are depicted in FIGURE 23.1.2,3
Tests for thyroid disorders2,3
Advances in technology have allowed the biochemical assessment of thyroid function to change dramatically in recent years with the introduction of the serum free thyroxine (T4) and the monoclonal TSH assays. With the highly sensitive TSH assays it is now possible to distinguish suppressed TSH levels (as in hyperthyroidism) from low and normal levels of TSH. However, the new assays are not foolproof and require interpretation in the context of the clinical picture. The serum TSH level is the most sensitive index of thyroid function and is the preferred test for suspected thyroid dysfunction. If necessary repeat TSH in 3–6 months.
Serum tri-iodothyronine (T3) measurement and serum free thyroxine (T4) can be useful in suspected T3 toxicosis where serum T4 level may be normal, and for monitoring patients with treated thyroid dysfunction.
The relative values are summarised in Table 23.1.