The Role of Late‐Night Salivary Cortisol in the Assessment of Endocrine Remission in Patients With Cushing's Disease After Pituitary Radiotherapy

ABSTRACT Context Pituitary radiotherapy (RT) is used for persistent/recurrent Cushing's disease (CD) after pituitary surgery. The utility of late‐night salivary cortisol (LNSC) in evaluating endocrine remission after RT is unclear. Objective To identify the clinical characteristics and outcomes of patients with CD after RT, in endocrine remission based on normal LNSC (group 1) or 24 h urinary free cortisol (UFC; group 2). Design and Setting Retrospective cohort, observational study in academic medical centre. Patients (16−86 years old, n = 75) with CD who underwent RT were studied; group 1 ( n = 16), group 2 ( n = 18), and 41 patients not in remission. Outcome measures included within‐group and between‐group changes (group 1 vs. group 2) in clinical characteristics, endocrine data and time to remission. Results Seventy‐five patients with CD, aged (median [range]: 50 years [16, 86], 71% female, BMI: 34.7 kg/m 2 [19.1, 62.5], 63% with macroadenomas) underwent RT and 34 (45.3%) entered endocrine remission, including 16 (21.3%) in group 1 and 18 (24%) in group 2 (median: 56 months). From RT to remission, there were decreases in BMI (group 1: −3.9 ± 0.7 kg/m 2 , p = 0.0001; group 2: −5.2 ± 1.9 kg/m 2 , p = 0.0123) and systolic blood pressure (group 1: −7.9 ± 3.9 mmHg, p = 0.03; group 2: −10.1 ± 4.5 mmHg ( p = 0.008). There were no between‐group differences in BMI, blood pressure, HbA1c, number of antihypertensive or antihyperglycemic agents, UFC, median time to remission, recurrence risk. Conclusion In patients with CD following RT, LNSC appears to be clinically equivalent to UFC in the assessment of endocrine remission. These patients can be followed with LNSC, which is easier for patients to collect.