Patients with the ectopic ACTH syndrome due to low-grade malignancies, such as a medullary thyroid carcinoma, carcinoid tumours or pancreatic endocrine tumours, develop typical features of Cushing's syndrome, because such patients survive for a sufficient period to develop the full-blown syndrome.
However, in the case of high-grade malignancies, such as small-cell carcinomas of the lung and uterus, the patient's condition becomes rapidly worse, which in turn makes it impossible to develop typical physical changes; such patients frequently present only an electrolyte imbalance, metabolic derangement and hyperpigmentation.
