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Chapter 11: Thyroid axis 427

Skin is thickened, oily and sweaty. Acne, sebaceous Accompanying hypopituitarism is treated as appro-

cysts and skin tags are common. Acanthosis nigricans priate with corticosteroids, thyroxine and gonadal
of the axillae and neck may occur. Hypertrichosis in steroids or gonadotrophins.
women.
Cardiovascular: Hypertension in 25% of patients,
Prognosis
and left ventricular hypertrophy and cardiomyopathy Follow-up is required for recurrence or loss of pituitary
leading to cardiac failure in about 15%. function. Acromegaly causes increased morbidity and
Organomegaly: Thyroid and salivary gland enlarge-
mortality mainly due to diabetes and cardiovascular dis-
ment, hepatomegaly. ease.
Diabetes in 40% of patients.

Thyroid axis
Macroscopy/microscopy
The tumour is solid and trabecular, often 1 cm in diame-
terby the time of diagnosis. Immunohistochemistry can The thyroid axis
be used to stain for GH.
Thyrotrophin-releasing hormone (TRH) is released
fromthehypothalamusepisodicallyandwithacircadian
Complications
rhythm. It stimulates the production of thyroid stimu-
Renal calculi occur in 10% as a result of the hypercal-

lating hormone (TSH) from the anterior pituitary gland.
ciuria induced by GH excess.
TSHisaglycoprotein, which binds to high-affinity re-
Local effects of a pituitary tumour include headache,

ceptors(TSH-R)inthethyroidgland.Thisinturnstimu-
and pressure effects such as bitemporal hemianopia.
latesiodideuptakebythethyroidgland,andthesynthesis
Panhypopituitarism may occur.
and release of thyroxine (T 4 ) and triiodothyronine (T 3 )
Increased risk of uterine tumours and possibly of

through activation of adenylate cyclase (see Fig. 11.6).
colonic polyps.
Somatostatin and dopamine agonists decrease TSH
secretionconverselydopamineantagonistsincreaseTSH
Investigations
secretion. Other hormones affecting the thyroid axis in-
IGF-I and GH levels are raised, but GH levels are un-

clude glucocorticoids, which in excess can impair the
reliable due to episodic secretion. An oral glucose sup-
sensitivity of the pituitary to TRH and hence reduce TSH
pression test is performed – a glucose load will fail to
secretion. Oestrogens conversely increase the sensitivity
suppress growth hormone production.
of the pituitary to TRH.
Imaging of the pituitary fossa by X-ray, CT or MRI.

If there is no evidence of a pituitary adenoma GHRH Production and action of the thyroid

may be assayed. hormones (T 3 and T 4 )
The epithelial cells of the thyroid gland produce thy-
Management roglobulin, which can be seen in the centre of thyroid
Wherever possible transphenoidal resection of the follicles and stains as pink ‘colloid’. TSH stimulates the

adenoma is the treatment of choice. Large tumours re-absorption of colloid by the cells and the production
may be resected by transfrontal craniotomy. Prior to of T 3 and T 4 .These hormones circulate in the blood
surgeryhypopituitarismmustbetreatedusingcortisol bound to thyroxine binding globulin (TBG) and albu-
and thyroxine. min. The majority of T 3 is converted from the less active
Octreotide or lanreotide, a long-acting somatostatin T 4 by peripheral tissues. Disorders of the thyroid axis are

analogue, may be used prior to surgery, following in- shown in Table 11.6 and Fig. 11.7.
complete resection or in elderly patients not fit for
surgery. Dopamine agonists may be added in refrac- Goitre
tory cases.
Irradiation may be used as an adjuvant to other ther- Agoitre is a visible or palpable enlarged thyroid. The

apies. enlargement may be generalised enlargement or diffuse