Hypothyroidism

Hypothyroidism

·        = Myxoedema if severe

·        Signs and symptoms:

o  Symptoms: Unhappy, no spark, ­weight, constipation, cold intolerance, menorrhagia (excessive menstruation, ¯T3 ® ¯oestrogen breakdown), lethargy, depression, dementia, ­sleep. Symptoms insidious and subtle (T3 receptors in nuclei of nearly all cells – govern metabolism, modulation of other hormones, O₂ consumption, regulation of protein synthesis, etc, etc)

o  Signs: bradycardia, dry skin and hair, goitre

o  Signs of myxoedema (­hydration of subcutaneous tissue): non-pitting oedema (eyelids, hands, feet), yellowing of skin (myxoedema absorbs carotene. Sclera unaffected), thickened tissues, voice change (oedema in vocal chords), hirsutism, carpal tunnel syndrome

o  If severe: slow, slurred speech (swollen tongue, slow thought), intention tremour (cerebellar effects), muscle weakness and pain, deafness (reverses with treatment), paranoid ideation, agitation, coarser hair, hair stops growing but no diffuse hair loss, slowly relaxing reflexes (contraction normal, relaxation slow – not specific to hypothyroidism), plethora (deep red cheeks), hypotension, ­ADH release ® hyponatraemia, normocytic normochromic anaemia, but no neuropathy (except secondary to, say, carpel tunnel)

o   Myxoedema coma: presents in coma with history of above symptoms. Exclude: alcoholism, epilepsy, diabetes mellitus, use of sedative medication, or clear suggestion of a fall predisposing to a subdural haematoma. With myxoedema may find pleural effusion, ascites, myocardial oedema (® arrhythmias), no focal neuropathies (unless concurrent CVA), possibly hypoglycaemia

·        Progression of primary hypothyroidism:

o  Normal TSH is 0.35 – 5.3

o  Prodromal hypothyroidism:

§  TSH 4.0 – 10.

§  fT4 usually still normal.  fT3 up marginally (failing gland ­ proportion of T3)

o  Partial hypothyroidism:

§  Early symptoms

§  TSH > 10 – 15

§  fT3 and fT4 falling, but may still be normal.  fT3 falls later than fT4

o  Severe:

§  With time develop myxoedema

§  TSH > 60.  fT4 < 6.0

·        Diagnosis:

o  Screening and severity: fT4 and TSH

o  Primary: TSH rises with minor changes in fT4 (before clinical features).

o  Secondary (rare): Test fT4. TSH remains in normal range but is inappropriately low for the fT4 level

o  Thyroid antibodies: almost all have positive antibodies at diagnosis

o  Thyroid scan not indicated

o  Normochromic macrocytic anaemia

·        Causes:

o  Spontaneous (autoimmune) 

§  Hashimoto‟s Thyroiditis: autoimmune disease, lymphocyte and plasma cell infiltration. Goitre. Usually older women. Often euthyroid + goitre. Invasion of polyclonal lymphocytes. Have oncocytes (cells with ­ mitochondria)

§  Spontaneous primary atrophic hypothyroidism. Autoimmune, = Hashimoto‟s without the goitre, associated with IDDM, Addison‟s and Pernicious anaemia. F:M = 6: 1

§  Woody Thyroiditis (Riedel‟s Thyroiditis): fibrous replacement of the thyroid

o   Iatrogenic:

§  Following thyroidectomy and radio-iodine treatment

§  Drug induced:  eg amiodarone (® hypo or hyper), lithium, iodine in expectorants

§  Not deep x-ray treatment to face and neck (does lead to nodular goitre),

o   Juvenile:

§  Dyshormonogenesis: eg partial deficiency of peroxidase ® gland hyperplasia ® restore

§  deficiency.  Expect: mild ­TSH, goitre and mildly hypothyroid

§  Agenesis/sublingual thyroid

§  Di George Syndrome.  Absent thymus, hypoplasia of parathyroid blands, lymphopenia

o   TSH deficiency: isolated, panhypopituitarism, hypothalamic disease

o   1% of Grave‟s go onto hypothyroidism

o   Iodine deficiency

o   High doses of iodine (eg ask about kelp)

·        Treatment:

o   Thyroxine. Takes 4 – 5 days to have any impact (ie not useful acutely). Review after 12 weeks. Adjust dose to keep TSH < 5 mu/L. T½ = 7 days so adjusting dose takes long time

o   Note: hypothyroid ® slow drug metabolism

o   If pre-existing heart disease, introduce very slowly.  Consider propranolol