Hyperthyroidism- assessment and management in primary care
TSH low T4 high / normal T3 high / normal ( unless on T4 treatment ). Direct physiological effect of the excess hormone & ↑↑ catecholamine activity. Thyrotoxicosis often used interchangeably with hyperthyroidism , it can be defined as ” excess thyroid hormone in the body, including exogenous intake of thyroid hormome preparations .Prevalence about 1 % to 2 % in women and 0.1 -0.2 % in men Happens in all ages 6 times more common in women
Subclinical hyperthyroidism- Low TSH but normal T4 and free T3 Possibly more prevalent than commonly believed- any symptoms of hyperthyroidism ? drugs ? Non-thyroidal illness ? -Repeat in 3-6 months time or earlier if elderly CV dis Non- thyroidal dis may have caused the initial abnormality.Persistent and unexplained – refer endocrinology
Two main causes of an overactive thyroid are Grave’s disease – peak incidence age 30 Toxic multinodular goitre. Primary hyperthyroidism- increased secretion of thyroid hormones causes a negative feedback resulting in ↓↓ TSH levels Secondary hyperthyroidism- abnormality is at the level of the hypothalamus or the pituitary gland. Grave’s disease – 75 to 80 % of cases ♦ autoimmune disease ♦ development of unique human autoantibodies to the thyroid stimulating hormone ( thyrotropin , TSH ) receptor ♦ this leads to unopposed stimulation of the thyroid gland causing ↑↑ ed synthesis and release of thyroid hormones and enlargement of the thyroid gland ♦ presents between 30-40 yrs ♦ ↑ ed risk with a family h/o hyperthyroidism those with an autoimmune dis e.g type 1 diabetes ♦ Presentation can be with hyperthyroidism + autoimmune features ie Grave’s ophthalmopathy and pretibial myxedema ♦ the disease has a waxing and waning course
Toxic multinodular goiter- Second leading cause excess thyroid hormone is released from multiple autonomously functioning nodules in the thyroid gland presents slowly , milder symptoms ↑↑ in the elderly
Other less common causes –Thyroiditis ♦ post-partum ♦ radiation ♦ sub-acute ( de Quervain ) ♦ chronic thyroiditis ( Hashimoto / lymphocytic ) Gestational thyrotoxicosis ( hCG stimulated ) Neonatal thyrotoxicosis Exogenous iodine Drugs e.g amiodarone Thyrotoxicosis factitia ( self treatment secretly with T4 ) TSH secreting pituitary tumors ( rare )
Can be quite insidious with patients often blaming other causes for their symptoms for e.g ♦ fatigue to work or family responsibility ♦ heat intolerance to weather ♦ weight loss to en effective diet ♦ dyspnoea and palpitation to being unfit Other presenting features can include ↑ appetite irritability and behaviour change restlessness malaise stiffness muscle weakness , proximal myelopathy , hyper-reflexia tremor oligomenorrhoea infertility , amenorrhoea diarrhoea itching , urticaria , vitiligo , diffuse alopecia deterioration in bl glucose control. polyuria loss of libido gynaecomastia onycholysis tall stature ( in children ) sweating eye signs ( lid lag or retraction ) Grave’s dermopathy ( rare ) splenomegaly , lymphadenopathy chorea ( rare )
Complications – Grave’s orbitopathy – difficult to treat and requires a multi-disciplinary approach Thyroid storm ( thyrotoxic crisis ) Atrial fibrillation Heart failure Osteoporosis Psychiatric features as anxiety , mood disorders , rarely frank psyhosis Thyrotoxic periodic paralysis ( very rare ) Adverse pregnancy outcomes
Thyroid storm-rare and life threatening event which may be precipitated by Infection Trauma Childbirth Diabetic ketoacidosis MI. Surgery Stroke Abrupt withdrawal of antithyroid medication or acute ingestion of thyroid medication-Sinus tachycardia or a variety of SV arrhythmia’s e.g paroxysmal atrial tachycardia , atrial flutter and AF often accompanied by various degrees of CCF. GI symptoms as vomiting , diarrhoea , intestinal obstruction, fever , CNS symptoms. dehydration jaundice electrolyte imbalance tremor shock goiter/ thyromegaly hyper-reflexia pretibial myxedema
Examine –pulse bp temp examine the gland CV exam Eye symptoms Tremor Reflexes Skin Palmar erythema Mental state is it drug related ?. Test- Check TSH Check TSH + FT4 and FT3 after 1-2 months- exclude non-thyroidal illness Inflammatory markers as CRP/ ESR if subacute thyroiditis is suspected Thyroid stimulating hormone receptor antibodies ( TRAbs ) FBC LFT Consider US if goiter suspected. ↑↑ SHBG Anaemia – can be microcytic , normocytic or macrocytic Mild granulocytopenia (in Grave’s disease ) ↑↑ AlkPo4 and liver transaminases.
If the aetiology of thyrotoxicosis is not clear – a radionuclide scan should be considered ( RAUI )- this is a measurement of thyroid function. Prescribe a beta blocker e.g propranolol and titrate the dose based on clinical response Propranolol 10-40 mg tds A calcium channel blocker can be considered for those who cannot take a beta blocker If on amiodarone / lithium – seek specialist advice Eye disease – if symptoms present issue lubricants and arrange early referral to ophthalmology Consider checking TFT every 4-6 weeks while awaiting specialist opinion.
Thyroid eye disease-dry eyes diplopia pain on eye movements proptosis ( exopthlamos ) lid retraction lid lag on downgaze chemosis conjunctival injection orbital fat prolapse karatopathy periorbital swelling optic neuropathy. For those with TED 85 % have hyperthyroidism , 10 % have hypothyroidism and 5 % euthyroid
Anti-thyroid drugs-Inhibit hormone synthesis ( thioamides ) ♦ propylthiouracil – usually not 1st line ( small risk severe liver injury ) ♦ carbimazole ( first line )- ling 1/2 life can be given once daily Alert- can cause neutropenia , agranulocytsosis Acute pancreatitis ( MHRA 2019 ) Pregnancy-unsafe Antithyroid drugs usually reduce symptoms within days Most patients would be euthyroid 4-6 weeks after treatment with carbimazole After this 2 strategies may be used Titration block regimen Block-replace regimen F/U – follow the specialist guidance , the treatment would be guided until e.g resolution of thyroiditis one year of remission in Grave’s disease TFT is stable after radioactive iodine or thyroid surgery Warn patients and advice to suspend antithyroid Rx if they develop mouth ulcers , fever, sore throat or other symptoms suggestive of infection
References Hyperthyroid disorders Terry F Davies et al Williams Textbook of Endocrinology , Chapter 12 , 369-415 Hyperthyroidism Nathanel J McKeown DO et al Emergency Medicine Clinics of North America New diagnosis of hyperthyroidism in primary care BMJ 2018 ;362 :k2880 CKS NHS Hyperthyroidism Kumar and Clarks Clinical Medicine – Edited by Parveen Kumar , Michael Clark Management of thyrotoxic crisis European Review for Medical and Pharmacological Sciences 2005 : 9 : 69-74 Fast Facts : Thyroid Disorders Evaluating and managing patients with thyrotoxicosis RACGP Volume 41 , No 8 , August 2012 Pages 564-572