Natural history of nonfunctioning adrenal incidentalomas: a 10-year longitudinal follow up study

Most data on natural history of nonfunctioning adrenal incidentalomas (NFAI) are provided by follow-ups up to 5 years. We conducted a 10.5 (9.1-11.9)-year follow-up study of NFAI in 67 participants (20 (29.9%) males, 47 (70.1%) females) of mean age 57.9 (52.3-63.9) years and BMI 27.42 (24.07-30.56) kg/m2). We also evaluated the associations between baseline body mass index (BMI) and changes of NFAIs’ characteristics at follow-up. Progression to mild autonomous cortisol excess (MACE) was observed in 15 (22 %) patients, with 14 of them having post overnight dexamethasone suppression test (ODST) cortisol between 50-138 nmol/L and only one >138 nmol/L. The progression rate was significantly higher in overweight and obese than in normal weighted subjects. Patients that developed MACE had significantly higher baseline mean cortisol after 1 mg ODST. Tumor enlargement ≥10 mm occurred in 8.9% of patients. All tumors had persistent radiological characteristics typical for adrenal adenoma. In comparison with reports of shorter observational periods, we observed higher growth rate ≥10 mm and higher progression rate from NFAI to MACE, particularly in overweight and obese subjects. We concluded that duration of the follow-up period is an important factor in characterizing the natural history of NFAI. Higher baseline BMI and higher baseline cortisol after ODST might predict the long-term likelihood of progression in hormonal activity. The magnitudes of observed progressions in growth or hormonal activity were clinical insignificant. Our long-term follow-up therefore clearly supports the general view that long term monitoring of patients with NFAI is not necessary.