Hypothyroidism

Essentials

• Identify the possibility of hypothyroidism when the patient's symptoms include fatigue, constipation, feeling cold, impaired memory and slow heart rate.
• The disease is common and its symptoms may be vague.
• Diagnosis of hypothyroidism and treatment of hypothyroidism originating in the thyroid gland (primary hypothyroidism) are tasks of the primary health care.
• Hypothyroidism is easy to confirm or exclude by determining TSH and free T4 (FT4) concentrations.
• Check readily whether the thyroid gland functions normally by determining TSH and FT4 concentrations before possible pregnancy and after pregnancy.
• Remember also that hypothyroidism can be the cause of high serum cholesterol or creatine kinase (CK) concentrations.
• In replacement therapy, a young or middle-aged patient usually feels best if TSH concentration is about 1-2 mU/l and FT4 concentration is close to the upper limit of the reference range.
• Elderly patients with e.g. angina pectoris or arrhythmias often are more susceptible to the effects of thyroxine. In them, the maintenance dose remains slightly lower and TSH concentration respectively a little higher.
• Ultrasonography has no role in the investigation of hypothyroidism (unless it is indicated by the findings on palpation).
• Thyroxine should not be used for the treatment of e.g. depression, low energy level or overweight in a person who is biochemically euthyroid.

Causes of hypothyroidism

Symptoms

• The symptoms and their severity vary in different individuals.
• In deep hypothyroidism the systemic symptoms include lack of initiative, fatigue, depressive mood, memory problems, slow motor functions and speech, feeling cold, constipation, weight gain and slow heart rate. The skin is dry, rough, cold or pale. Hair may become rough, and there is hair loss. The symptoms may also include muscle weakness, ache and stiffness.
• The menstrual cycle may be disturbed.
• In the elderly the clinical picture is often atypical with slowing and depression that may simulate dementia.
• In young women the first symptom may be amenorrhoea or infertility and/or hyperprolactinaemia.

Diagnosis Screening for Thyroid Disease and Treatment of Subclinical Hypothyroidism

• See article on examining a patient with a thyroid complaint Examining a Patient with a Thyroid Complaint.
• The thyroid gland is palpated (size, concistency).

Thyroxine treatment Effect of Thyroxine Therapy on Serum Lipid Levels in Subclinical Hypothyroidism, Thyroid Hormone Replacement for Subclinical Hypothyroidism

• Thyroxine substitution is always indicated if serum TSH concentration is increased and FT4 concentration is decreased.
• In subclinical hypothyroidism, therapy is started if TSH concentration is over 10 or if the patient is pregnant. If serum TSH concentration is permanently but only slightly increased (> 3.6-4 mU/l), following factors support the initiation of therapy: symptoms suggesting hypothyroidism, young age, pregnancy, increased concentration of TPO antibodies, goitre and hypercholesterolaemia.
  • In mild subclinical hypothyroidism, treatment decisions are made individually. Before starting the possible thyroxine substitution, a repeat TSH measurement should be performed. According to current recommendations, subclinical hypothyroidism (TSH < 10 mU/l, FT4 within reference range) should not be treated in very old persons.
  • Before starting permanent thyroxine substitution, it is often advisable to carry out a therapeutic trial of 3-6 months.
• In young patients the initial dose of thyroxine is 50-100 µg/day. If the patient has been hypothyroid for a long time, the dose is gradually increased by 25 µg every 2 weeks until the dose 100 µg/day is reached.
• The maintenance dose correlates with the patient's body weight. The usual maintenance dose is approximately 100-200 µg/day. In subclinical hypothyroidism, a lower maintenance dose is usually required.
• TSH is checked at the earliest 4 weeks from the latest dose increase. On that occasion, the maintenance dose is adjusted to a suitable level. The patient often feels well if TSH concentration is 1-2 mU/l and FT4 is within the upper third of the reference range.
• In the elderly and in patients with ischaemic heart disease the initial dose is 25 µg/day. The dose is gradually increased at 3 to 4 week intervals.
  • In patients who are elderly or who have a cardiac disease, the maintenance dose is often left lower than usual, in which case TSH concentration is close to the upper limit of the reference range.
• After a change in the dose of thyroxine, serum FT4 and TSH are determined after 4 weeks at the earliest because the concentration of TSH changes slowly. When the maintenance dose has been established, TSH is determined every 1 to 2 years, e.g. in conjunction with prescription renewal. In full substitution, the dose usually remains stable.
• In controversial cases (e.g. in possibly transient hypothyroidism) serum TSH should be determined 6 weeks after discontinuation of treatment. If serum TSH rises above the reference range permanent thyroxine substitution is indicated.
• Thyroxine dose of thyroid cancer patients Primary Care Follow-Up of Thyroid Cancer after Treatment who are followed up in specialized care must not be changed in the primary health care.
• Thyroxine is taken in the morning as a single dose on an empty stomach.
  • Certain drugs, especially iron and calcium medications, disturb the absorption of thyroxine; such medications should not be taken until at least 4 hours after the intake of thyroxine.
  • Oestrogen replacement therapy has the same effect as pregnancy: need for thyroxine increases with up to one third.