Application Of ¹⁸F-FDG PET/CT In Clinical Diagnose And Glucose Metabolism Research Of Cushing's Syndrome

OBJECTIVE:To investigate the value of ¹⁸F-FDG PET/CT in the localization diagnosis of ACTH-dependent Cushing's syndrome and to study the glucose metabolism disorder in patients with Cushing's syndrome.METHODS:This study retrospectively included 47 patients with ACTH-dependent Cushing's syndrome who underwent ¹⁸F-FDG PET/CT examination from November2010 to January 2018 in our center,and compared the diagnostic efficacy of high-dose dexamethasone suppression test?HDDST?,pituitary MR,bilateral inferior petrosal sinus sampling?BIPSS?and ¹⁸F-FDG PET/CT.In addition,52 patients of Cushing's syndrome undergoing ¹⁸F-FDG PET/CT examination in our center were also reviewed as comparisons in the same period.They were divided into non-diabetic group?CS-N?and diabetic group?CS-D?respectively.The SUVmax and thickness of skeletal muscle and fat were compared in each group.Correlation analysis of blood cortisol,adrenocorticotropic hormone?ACTH?with indicators of glucose,lipid,bone and growth metabolism were performed.The differences of clinical parameters and imaging parameters between CS-N and CS-D groups were compared to investigate the main risk factors for diabetes in patients with Cushing's syndrome.RESULTS:In the diagnosis of Cushing's syndrome,blood ACTH level was the main factor affecting localization.It could be a localization diagnostic criterion that blood ACTH levels were 2 times higher above the upper limit of the normal range.There was a certain correlation between pituitary SUVmax of ¹⁸F-FDG PET/CT and HDDST in Cushing disease patients.There was a significant positive correlation between adrenal SUVmax and ACTH logarithm?r=0.910,p<0.01?.Of the 20 neuroendocrine tumors,11 were mediastinal carcinoid,4 were pulmonary NETs,4 were pancreatic NETs,and1 was olfactory neuroblastoma.Their SUVmax was 7.1±2.4?3.5-10.1?,2.0±0.1?1.9-2.2?,13.2±8.3?4.8-26.4?,10.6,respectively.Mediastinal EAS tend to relapse and metastasis?45.5%?,and recurrent lesions frequently presented low SUVmax?2.0-3.2?.Pulmonary nodules'morphology and its SUVmax could help distinguish ectopic ACTH Cushing's syndrome and infection.Particularly,the ¹⁸F-FDG PET/CT had a sensitivity of up to 100%in the diagnosis of pancreatic EAS,and the specificity was even higher than that of pancreatic MR.In addition,¹⁸F-FDG PET/CT also showed important diagnostic value in the diagnosis of peripheral and central bifocal lesions.In terms of glucose metabolism,¹⁸F-FDG PET/CT imaging showed that peripheral insulin resistance in patients with Cushing's syndrome was much lower than that in patients with type 2 diabetes when plasma glucose levels were same.SUVmax of biceps,psoas,subscapularis,infraspinatus muscles in CS-D group were higher than that in other groups.Fat tissues were site-specific:There was a decreased SUVmax of the subcutaneous fat in CS-D group,and an increased SUVmax of the abdominal fat in the CS-N group.In terms of structure,patients with Cushing's syndrome have extensive skeletal muscle wasting and fat accumulation;latter mainly occurred in the neck subcutaneous fat and abdominal cavity fat,and it was another main risk factor for diabetes in CS patients.The growth hormone,osteogenic activity had a certain correlation with the glucose uptake of skeletal muscle and fat in CS patients.CONCLUSIONS:¹⁸F-FDG PET/CT is of great significance in the diagnosis and functional assessment of ACTH-dependent Cushing's syndrome.Cushing's syndrome-induced diabetes is mainly due to impaired islet cell function,while insulin resistance is not significant.Muscle wasting and increased muscle glucose-uptake is widespread in CS patients.The fat accumulation in CS patients is mainly in neck subcutaneous and abdominal cavity fat.Growth metabolism and osteogenic activity plays an important role in these changes of skeletal muscle,fat of Cushing's syndrome patients.