HYPOTHYROIDISM (MYXOEDEMA)

This is common and easy to treat

Epidemiology:        Predominant age >40, female:male = 5-10:1

Risk factors:        Increasing age
                     Autoimmune disease
                     Previous postpartum thyroiditis
                     Previous head or neck irradiation

Associated cond:     Hyponatraemia, anaemia, DM, hypoparathyroidism, myasthenia
                     gravis, vitiligo, hypercholesterolaemia, mitral valve prolapse,
                     depression, ischaemic heart disease

Symptoms:            tiredness, lethargy, increased weight, constipation, dislike of cold,
                     menorrhagia, hoarse voice, depression, poor concentration, poor
                     cognition, myalgia

Signs:               Bradychardia, dry skin, goitre, slow relaxing reflexes, CCF, non-
                     pitting oedema (eyelids, hands, feet), toad like face, pericardial
                     effusion, peripheral neuropathy, cerebellar ataxia.

    Primary hypothyroidism
        o TSH elevated
        o Serum free T4 decreased
    Central hypothyroidism
        o TSH low
        o Serum free T4 decreased
        o Impaired TSH response to TRH
    Severe hypothyroidism
        o Anaemia (normochromic macrocytic)
        o Elevated cholesterol
        o Elevated CPK, LDH, AST (due to abnormal muscle membranes)
        o Hyponatraemia
    Subclinical hypothyroidism
        o TSH elevated
        o T4 normal

Differential diagnosis:      Nephrotic syndrome, chronic nephritis, depression, CHF,
                             primary amyloidosis

Primary hypothyroidism:
Post thyroidectomy or radioiodine treatment
Drug induced: Anti thyroid drugs; amiodarone, lithium, iodine.
Subacute thyroiditis: temporary hypothyroidism after hyperthyroid phase
Iodine deficiency: poor diet
Genetic: with deafness (Pendred’s syndrome)
Dyshormonogenesis: Autosomal recessive e.g. from peroxidise deficiency. Look for
increased radioiodine gland uptake displaced by potassium perchlorate

Hashimoto’s thyroiditis: autoimmune disease in which there is lymphocyte and plasma
cell infiltration. Usually in women aged 60-70 years old. Often euthyroid, or occasionally
initial period of hyperthyroidism (hashitoxicosis). Autoantibody titres are high. Treat as
below if hypothyroid, or to reduce goitre if TSH high. Associated with other autoimmune
Spontaneous primary atrophic hypothyroidism: common, autoimmune disease which is
essentially Hashimoto’s without the goitre and is associated with type I diabetes,
Addisons disease or pernicious anaemia.

Secondary hypothyroidism:
Hypopituitarism: is very rare

                                    If healthy and young:
Levothyroxine (T4), adjust 6 weekly by clinical state to normalise but not suppress TSH.
Once normal check TSH yearly. Metabolisom of levothyroxine is increased by enzyme-
                          If elderly or ischaemic heart condition
Start with a lower dose. Caution: levothyroxine may precipitate angina or MI.

                     If diagnosis is in question or T4 already given
Stop T4, and re-check TSH in 6 weeks.

Myxoedema Coma:
Signs and symptoms: looks hypothyroid, hypothermia, hyporeflexia, hypoglycaemic,
bradychardia, coma, seizures. Causes: prior surgery or radioiodine for hyperthyroidism.
Precipitants: infection, MI, stroke, trauma. Examination: goitre, heart failure, cyanosis
    Take bloods for T3 T4, TSH, FBC, U+E, cultres and cortisol
    Take arterial blood for PaO2
    Give high flow O2 if cyanosed
    Correct hypoglycaemia
    Give T3 slowly IV. Be cautious this may precipitate manifestations of
        undiagnosed ischaemic heart disease.
    Give hydrocortisone IV (vital if pituitary hypothyroidism is suspected)
    IVI 0.9% saline. Caution: avoid precipitation heart failure
    If infection give antiobiotic

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