Cushing's disease: risk of recurrence following trans-sphenoidal surgery, timing and methods for evaluation

The treatment of choice for Cushing's disease (CD) is trans-sphenoidal surgery (TSS). However, TSS is not always curative and, even when curative it is associated with a substantial rate of recurrence. Published recurrence rates vary between 5 and 20%; half of these recurrences appear within 5-years and the remaining half within or even after 10 years post-surgery. A low or undetectable cortisol in the immediate post-op period is regarded as the best criterion of remission. However, low post-op cortisol levels do not accurately predict long-term remission. Moreover, there are no other robust predictors providing certainty about the long-term outcomes. Interestingly, several studies have shown that the desmopressin test performed in the early post-op period may have some promise in predicting more precisely the risk of recurrence. In view of the lack of robust ways to predict long-term outcomes, current guidelines suggest that every patient in remission should be monitored for the possibility of recurrence. The methods used to detect recurrence are similar to those used to assess the cortisol secretory status and include assessment of: (i) abnormal circadian rhythm by late night salivary cortisol (LNSC) or midnight serum cortisol; (ii) impaired cortisol feedback by the dexamethasone suppression test and; (iii) increased 24-h bioavailable cortisol by urinary free cortisol. The timing of evaluation begins when HPA axis recovers, and then annually or sooner in case of clinical suspicion. Currently LNSC is regarded as the earliest and most sensitive biochemical alteration in detecting recurrence; a major caveat for LNSC, however, is its great variability. In practice, the diagnosis of recurrence is a challenge due to the fact that recurrence is usually a slow process with apparent clinical manifestations that may be delayed and alterations of classical biomarkers that may be delayed as well.