[Low thyrotrope hormone: a new entity]

The combination of the TRH stimulation of TSH release with the plasma iodide (PII) increase test, which gives a physiological measure of TSH basal activity, allows characterization of a syndrome we have called a low pituitary TSH reserve. These patients were euthyroid, had a normal PII increase test but a mild or no response to TRH. It was chiefly found in acromegaly and diabetes mellitus, after prolonged high levels of thyroid hormones or hypophysectomy. It appears to be a transient state between normal and abnormal thyrotropin function. So the absence of TSH increase after TRH injection can be of diagnostic value only when other tests of thyrotropin function are performed.