Euthyroid Hyperthyroxinemia: a Case Report

Med. J. Malaysia Vol. 42 No. 1 March 1987

EUTHYROID HYPERTHYROXINEMIA: A CASE REPORT

M. RAMANATHAN

SUMMARY tion.was otherwise normal and in particular there This report deals with the problems ofa young was no other signs of thyrotoxicosis. He had no man who was clinically euthyroid but bioche tremor. Pulse rate was 80/minute and regular. mically hyperthyroid. The possibility ofperipheral There was no muscle wasting or evidence of resistance to thyroid hormones to explain this proximal myopathy. paradoxical state is discussed. The importance Routine investigations including haemoglobin, of recognising this condition to avoid the random blood sugar, blood urea, serum electro erroneous diagnosis of thyrotoxicosis and in lytes, chest X-ray and ECG were within normal limits. Serum thyroxine (T and triiodothyronine appropriate therapy is stressed. 4) (T3) done by his general practitioner were noted INTRODUCTION to be high but the actual results were not available. These measurements were therefore repeated: The measurement of serum thyroxine (T4) concentration is the most commonly used test to Serum thyroxine (T4) - 169 nmol/I (normal diagnose hyperthyroidism in cl in ical practice. range 60 - 130 nmol/l l: Serum triiodothyronine However there are a number of other conditions (T3) 5.71 nrnol/l (normal range 1.23 - 3.38 besides thyrotoxicosis which could give rise to an nrnol/l ). elevated serum thyroxine level. One such condi He was treated as a case of thyrotoxicosis with tion is peripheral resistance to thyroid hormones carbimazole 45 mg daily and propranolol 20 mg as illustrated by the case under discussion. th ree times a day and reviewed after eight weeks. He reported that he had stopped the medications CASE HISTORY a week before the follow-up as he felt that they were doing him "no good". A 27-year-old construction site worker was referred to the hospital for thyrotoxicosis. He He had developed severe intolerance to cold, presented with a history of having noticed a goitre change in voice and lethargy about a month after for a year which had remained static in size. being on treatment. He had also gained 10 kg over th is period. He vol unteered a vague history of heat into lerance and occasional palpitation for about three On examination, his pulse was 55/minute, months prior to seeking medical advice. He had no regular and reflexes were normal. It was felt that he had developed drug induced hypothyroidism other symptoms of thyrotoxicosis. His past medical history was unremarkable; he denied and his medications were stopped completely. abuse of alcohol, drugs or tobacco. There was no His thyroid function tests done a week later family history of thyroid disorders. were as follows: Serum thyroxine (T4) 86 nrnol/l (normal range 60 - 130 nmol/I); Serum triiodo On examination he had a diffused soft non thyronine (T3) 5.3 nmol/I (normal range 1.3 tender goitre with no bruit. The physical examina- 3.2 nrnol/l}: Serum TSH 6.1 mlU/1 (normal

M. Ramanathan, MRCP (UK) range>7.3mIU/1. Consultant Physician, General Hospital He was reviewed after six weeks and was 75400 Me/aka, Malaysia found to be clinically euthyroid but serum free

65 thyroxine done at this stage was noted to be high TABLE I at 31 pmol/l (reference range 9.4 - 25.0 pmol/I CAUSES OF ELEVATED SERUM TOTAL THYROXINE

Amerlex-M Free T4 R lA kit). Since then, he has Hyperthyroidisim been reviewed periodically for the past one year Increased serum protein binding and is euthyroid clinically. His pulse rate during Increased TBG concentration this period was between 70 - 85 beats per minute Non-Thyroidal illnesses and regular. His weight has remained constant at Liver disease 67 kg. The goitre has not increased in size and Acute intermittent porphyria there is no bruit. Drugs 5-Flurouracil Clofibrate DISCUSSION Amphetamines This patient was initially treated for thyrotoxi Amiodarone Iodinated radio contrast dyes cosis based on the clinical history and a reportedly raised thyroid hormone level. He had only minimal Transient hyperthyroxinaemic states (and vague) complaints to suggest hyperthyroi Acute medical illness Acute psychiatric illness dism but these may be consistent with early High altitude exposure thyrotoxicosis or T 3-toxicosis. A repeat thyroid hormones assessment showed raised serum T 3 with Peripheral tissue resistance to thyroid hormones borderl ine raised T4 level supporting the diagnosis (Modified from Ladenson P.W.):! of early thyrotoxicosis. One of the common causes of raised serum T4 in After about seven weeks on the anti-thyroid euthyroid patients is related to serum al bumin therapy, the patient noted features suggestive of or thyroid-binding pre-al bumin abnormal ities.' hypothyroidism. The cl inical impression at th is This familial dysalbuminaemia hyperthyroxinemia stage was that this (iatrogenic) hypothyroidism (FDH) is unlikely in this patient as the condition was related to the rather high dose of carbimazole is an autosomal dominant svndrome' and there (45 mg daily) prescribed for the patient consider was no history of similar thyroid disease in the ing that he had only minimal symptoms and the patient's family (though thyroid hormone levels serum T4 was only siightly raised. However, should be assessed to be certain). In the FDH thyroid function tests done two weeks after syndrome usually only serum T4 is raised while stopping treatment showed normal serum T4 serum T 3 is with in normal ranqe.' Th is is because and more surprisingly an above-normal serum T 3 in this disorder the abnormal albumin molecule concentration. Serum free T4 done subsequently has an increased affinity for T4 but not for T3.1 when the patient was cl inically euthyroid was In this patient, serum T3 was raised on several also found to be raised. occasions. This development of hvpothvroidisrn and the One cause of euthyroid hyperthyroxinemia is results of tests showing normal T4' high T3 and related to peripheral tissue resistance to thyroid high serum free T4 while the patient was clinically hormones. This syndrome was first described by euthyroid even after periodic reviews would Refetoff in 1967 in three sibl ings of consan suggest that the patient may not be thyrotoxic guinous parents." Subsequently a number of even though the serum thyroid hormones were sporadic as well as familial cases with autosomal raised. dominant inheritance were reported.' There was no history to suggest acute illness, Patients with this syndrome typically present drug ingestion or Iiver disease to account for the with a goitre but with no clinical evidence of raised thyroid hormones. thyrotoxicosis. Serum thyroid hormones (both A condition referred to as euthyroid hyper the total and free concentrations) are classically thyroxinemia has been described and is associated raised. The case under discussion who presented with a number of clinical situations (Table I). with a goitre and raised thyroid hormone levels

66 but with minimal symptoms of thyrotoxicosis thyroid hormones. This rare syndrome should be may fit into th is rare syndrome. considered in a patient presented with a goitre and raised serum thyroid hormone levels but The exact defect leading to peripheral resis with minimal or no clinical features of thyroto tance to thyroid hormones is not known. Some xicosis. As a corollary, one should be wary of authors postulate an abnormal T3 binding to tissue treating a patient for thyrotoxicosis based solely receptors with postbinding defects." While others on thyroid hormone levels without collaborative have suggested qualitative defect of nuclear T3 clinical features suggestive of hyperthyroidism. receptors and/or a defect in the transport of thyroxine across the plasma membrane." It is likely that there are several different defects which ACKNOWLEDGEMENT collectively lead to the "common clinical end point of peripheral resistance to the thyroid "I would like to thank the Director General hormones"? of Health Malaysia for permission to publish this article and also Magdelene Hendroff for secre Confirmation of this syndrome in a patient tarial assistance". would depend firstly on the exclusion of other causes of raised thyroid hormones in a patient who is clinically euthyroid and secondly on REFERENCES hormonal response at cellular level. The latter 1 Ladenson P W. Diseases of the thyroid gland. Clinics would entail the use of receptor assays and the In Endocrinology And Metabolism 1985; 14( 1): 145 assessment of postreceptor events such as cyclic 169.

AMP generation after exposure to thyroid hor 2 Borst GC, Eil C, Burman K D. Euthyroid hyper mones. Since these specialised tests are not thyroxinemia. Annals Of Internal Medicine 1983; 98: generally available in routine laboratories, diag 366-378. nosis of tissue resistance to thyroid hormones 3 Croxon MS, Palmer BN, Holdaway IM, Frengley PA, as in th is patient would have to be by exclusion Evans MC. 'Detection of familial dysalubinaemia of other causes of euthyroid hyperthyroxinemic Iiyperthyroxinemia. Br Med J 1985; 290 : 1099 state and on clinical observations over a period of 1102. time. 4 Wortsman J, Premachan DM BN, Williams K et. al. Familial resistance to thyroid hormone associated In conclusion, this case illustrates a possibility with decreased transport across the plasma mem of peripheral resistance to thyroid hormones in a brane. Annals Of Internal Medicine 1983; 98 : 904 clinically euthyroid patient with raised serum 909.