Long-term follow-up of low-dose external pituitary irradiation for Cushing's disease.

Twenty-four patients (three male) with Cushing's disease, aged between 11 and 67 years, were treated with low-dose external pituitary irradiation (20 Gy in eight fractions over 10-12 days) and followed for between 13 and 171 months (median 93 months). Eleven patients (46%) went into remission 4-36 months after irradiation, but five subsequently relapsed. Two of these received no further active treatment, one underwent successful pituitary surgery, one underwent a second course of low-dose external irradiation (as yet unsuccessful) and one has been treated with metyrapone for a total of 75 months. One of the 13 patients who did not respond received a further course of low-dose pituitary irradiation with prompt remission and two have received metyrapone for 41 months and 15 years without ill effect. One patient died from cerebrovascular disease. The remaining nine patients underwent bilateral adrenalectomy (one after unsuccessful pituitary surgery) with rapid resolution of hypercortisolism. Five of these patients have developed hyperpigmentation and elevated ACTH levels (range 505-1150 ng/l). A pituitary microadenoma has been demonstrated on CT scan in three and successfully removed by microadenomectomy. In the present series, the low incidence of radiation-induced hypopituitarism and absence of other complications attributable to radiotherapy suggest that low-dose pituitary irradiation may be a useful treatment option in selected patients. However, long-term follow-up has demonstrated a high relapse rate and failure to prevent Nelson's syndrome in adrenalectomized patients, indicating that it should not be used as primary treatment in preference to selective adenomectomy.