ACTH-dependent Cushing’s syndrome (CS) is associated with significant morbidity and mortality if untreated and diagnosis is often challenging. This study aims to evaluate the experience in a single centre: i) the screening investigations used to diagnose ACTH-dependent CS; ii) the utility of inferior petrosal sinus sampling (IPSS) and MRI pituitary in differentiating pituitary from non-pituitary ACTH-dependent CS; iii) early post-operative serum cortisol level in predicting remission in Cushing’s Disease (CD).
All patients diagnosed with ACTH-dependent CS between 2001-2015 at RMH were reviewed. Data were collected using the Biogrid platform and medical records.
In total, twenty-four patients were diagnosed with CS in this period. Amongst them, 23 patients had CD (F:M ratio 15:9). The 1mg overnight dexamethasone suppression test (DST) was the most sensitive screening test (range:136-939nmol/L; sensitivity 100%) followed by the 24-hour urinary free cortisol (UFC) (sensitivity 88%;p<0.003) and late night salivary cortisol(sensitivity 83%;p=0.10).
IPSS was performed in 15 patients and the inferior petrosal sinus:periphery (IPS:P) ACTH ratio ≥2 at baseline or ≥3 post-CRH were both positive in all cases. 13/15 cases had histologically proven CD post operatively. A pituitary adenoma was visible on MRI in 10/15 cases of confirmed CD.
Post-operative morning cortisol level (Day 1-3) was greater in patients with persistent CD (median 611, IQR 408-872 nmol/L) than those who achieved remission post operation (median 78, IQR 43-227 nmol/L;p=0.01). This level also appeared greater in those with recurrence (median 668, IQR 400-670nmol/L) compared to those in remission after 63.7months follow-up with median time to recurrence of 25.2 months, however this result did not reach statistical significance( (p=0.154).
The 1mg DST was the most sensitive screening test for ACTH-dependent CS. A positive IPSS result was useful in confirming the diagnosis of CD. Post-operative Post-operative morning cortisol levels (Day 1-3) may held prognostic value.