Clinical, biochemical and immunological characteristics of relapsers and non-relapsers of thyrotoxicosis treated with anti-thyroid drugs

Objectives. This study aims to correlate clinical, biochemical and immunological factors seen at diagnosis of thyrotoxicosis with subsequent relapse within 5 years. Design. Retrospective review of case notes, and biochemical assessment at least 5 years after cessation of treatment. Setting, A large general hospital endocrine clinic. Subjects, Patients presenting with a first episode of thyrotoxicosis between 1988 and 1991 who were treated with antithyroid drugs for at least 18 months. Main outcome measures. Relapse was determined by examination of hospital records, general practice records, patient questionnaire and thyroid function tests. Results. A total of 216 subjects presented for the first time with thyrotoxicosis, of whom 89 (41.2%) suffered a relapse of the disease. On univariate analysis, clinical factors associated with increased relapse include younger age at diagnosis, goitre, marked tachycardia, requirement for higher maintenance dose of carbimazole, higher FT4 levels at diagnosis and smoking. Factors not predictive of relapse include presence of thyroid eye signs, positive family history, atrial fibrillation or congestive cardiac failure, acropachy or pretibial myxoedema, and presence or absence of thyroid autoantibodies. Logistic regression analysis showed relapse was predominantly determined by an FT4 > 56.2 nmol L-1, pulse rate > 110, presence of goitre and a positive smoking history (R-2 = 0.3, P < 0.001). Presence of these four factors predicted relapse in 76 (85.4%) of the 89 patients who relapsed. Conclusions, Increased 'toxicity' of thyrotoxicosis, goitre and smoking are associated with relapse of thyrotoxicosis, and this may be helpful in determining which patients may be better managed with early ablative therapy.