Objective: To report a series of newly diagnosed thyrotoxic patients with concurrent acute psychosis, and to assess the association between the two disorders. Design: Retrospective study of thyrotoxic patients with associated psychosis ('thyrotoxic psychosis'; TP) requiring inpatient psychiatric care. New Zealand thyrotoxicosis annual incidence figures and first psychiatric admission rates for affective psychosis were utilised to statistically assess the co-occurrence of thyrotoxicosis and affective psychosis. Patients and Methods: During the 20-year study period, 18 inpatients (16 women and 2 men), mean age 54 years, with TP were identified. No patient had a past history of thyrotoxicosis, but four had required psychiatric inpatient care many years earlier. Thyrotoxicosis was documented by radioimmunoassay of thyroid hormone levels, and thyroid scintiscan. Psychiatric manifestations were classified using ICD9 criteria. Results: Thyroid hormone levels were markedly elevated in more than half of our TP patients. All younger patients had Graves' disease, and most older patients toxic nodular goitre. All patients were treated with antithyroid drugs, and all but one subsequently received 131 I therapy. Two patients were not mentally ill when thyrotoxicosis was diagnosed, but suffered major mood swings when thyroid hormone levels were falling. There was no specific psychiatric clinical picture but affective psychoses were commonest -seven depression, seven mania. The other diagnoses were two schizophreniform, one paranoid, and one delirium. Initially, neuroleptic medication was used in all but one patient, and during long-term follow-up (median 11 years) more than half our series had remained well with no further psychiatric problems. Statistical analysis was restricted to thyrotoxic patients with first psychiatric hospital admission for affective psychosis. During the 20-year period, there were nine thyrotoxic patients (95% confidence interval 4.5-17.1) with concurrent affective psychosis requiring first admission, and the calculated expected number was only 0.36. These findings indicate a clear association well above chance co-occurrence. Conclusion: TP is not a specific clinical picture, but affective psychoses are commonest. Statistical analysis of thyrotoxic patients with concurrent affective psychoses showed an incidence well above chance co-occurrence. It appears that thyrotoxicosis may be a precipitant of acute affective psychosis.

Statistical analysis has shown that long-term lithium therapy is associated with an increased risk of thyrotoxicosis. LiAT is a heterogeneous condition with differing underlying thyroid pathologies and the mechanisms remain uncertain. The management of LiAT should initially be with antithyroid medication, and 131I therapy should be given only to patients who do not obtain long-term remission.

The placental transfer of 35S-labelled methimazole (MMI), carbimazole and propylthiouracil (PTU) has been examined in the rat in late pregnancy and in patients undergoing therapeutic abortion. Although rapid equilibrium of fetal and maternal serum radioactivity (FS:MS ratio 1:1) occurred after iv administration of 35S-carbimazole or 35S-MMI in rats, a persistent fetal to maternal ratio of less than one was observed after 35S-PTU administration. Results from human studies after a single oral dose indicate that, as in the rat, the placenta appeared to be more permeable to 35S-MMI than to 35S-PTU as shown by the marked difference in fetal serum:maternal serum ratios and amounts accumulated in the fetus. Localization of radioactivity in the human fetal thyroid was also observed after administration of 35S-labelled MMI, carbimazole or PTU.

In a 3-year (1983-1985) epidemiological study of thyrotoxicosis in North Canterbury, New Zealand, the annual incidence was 25.8 per 100,000 (female 40.7, male 10.5). Thyroid scintiscanning showed that 64% had diffuse hyperplasia (DH), 27% toxic multinodular goitre (TMG), 7% toxic uninodular goitre (TUG), and 2% zero uptake. The calculated annual incidence of toxic diffuse goitre (DH) was 15 per 100,000, and for toxic nodular goitre (TMG and TUG combined) was 8 per 100,000. The age-related incidence for toxic diffuse goitre peaked in middle life whereas toxic nodular goitre showed an increasing incidence with age. There was no significant seasonal variation or rural/urban difference in incidence. Analysis of geocoded addresses did not identify areas of high incidence. The variable duration of symptoms prior to diagnosis limits the search for possible environmental trigger factors. North Canterbury was an endemic goitre area prior to the introduction of iodized salt 50 years ago, and the incidence of toxic nodular goitre is likely to fall in future.

No abstract