Clinical and subclinical hypothyroidism in patients with chronic and treatment-resistant depression.
OBJECTIVE
To investigate the relationship between hypothyroidism and treatment-resistant depression (TRD).


METHODS
A retrospective case audit of 93 inpatients of a specialist Mood Disorders Unit. Patients referred with TRD were sub-classified into 'adequate' or 'inadequate' prior treatment groups on the basis of pre-established criteria, and compared with a 'non-TRD' control sample. Grades I (clinical) and II (subclinical) hypothyroidism were determined by review of relevant thyroid indices.


RESULTS
Patients had chronic depressive disorders (sub-group means of 57.5-82.2 weeks of illness). Of those patients referred with TRD, 22% (10/46) had evidence of clinical or subclinical hypothyroidism compared with 2% (1/47) of the non-TRD patients (p < 0.01). A gradient in the rates of grade I hypothyroidism was observed with the adequately-treated TRD patients having the highest rate (13%), the inadequately-treated TRD patients having an intermediate rate (7%), and the non-TRD patients having the lowest rate (2%). Consistent with this view, the inadequately-treated TRD group had the highest rate of grade II hypothyroidism (p = 0.01) and tended to have higher thyroid stimulating hormone (TSH) values (p = 0.06). Differences in the rates of hypothyroidism could not be accounted for by differences in age or prior exposure to lithium and/or carbamazepine. Duration of the depressive episode was negatively correlated with both the free thyroxine indices (r = -0.25, P < 0.05) and TSH levels (r = -0.32, p < 0.01).


CONCLUSIONS
This study suggests that relative hypothyroidism may play a role in the development of some treatment-resistant depressive disorders.
Hickie
I
I
School of Psychiatry, University of New South Wales, Academic Department of Psychiatry, St George Hospital and Community Service, Kogarah, Australia.
Bennett
B
B
Mitchell
P
P
Wilhelm
K
K
Orlay
W
W
D000328:Adult; D000368:Aged; D000928:Antidepressive Agents / Q000627:therapeutic use; D002908:Chronic Disease; D015897:Comorbidity; D003430:Cross-Sectional Studies; D003866:Depressive Disorder / Q000175:diagnosis / Q000188:drug therapy / Q000453:epidemiology*; D004351:Drug Resistance; D005067:Euthyroid Sick Syndromes / Q000175:diagnosis / Q000188:drug therapy / Q000453:epidemiology*; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000175:diagnosis / Q000188:drug therapy / Q000453:epidemiology*; D015994:Incidence; D008297:Male; D008875:Middle Aged; D019965:Neurocognitive Disorders / Q000175:diagnosis / Q000188:drug therapy / Q000453:epidemiology*; D009517:New South Wales / Q000453:epidemiology; D012189:Retrospective Studies; D013960:Thyroid Function Tests
D000928:Antidepressive Agents