SAT-044 - A Case of Ectopic Cushing Syndrome Secondary to A Neuroendocrine Pulmonary Nodule Treated with Stereotactic Body Radiation Therapy

Background:
Ectopic Cushing syndrome (ECS) accounts for around 15% of endogenous Cushing syndrome cases. The majority are caused by bronchial neuroendocrine tumors followed by small-cell lung carcinomas. We report a case of a 42-year-old man who developed ECS secondary to a lung nodule that responded to medical treatment and stereotactic body radiation therapy (SBRT).

Case:
A 42-year-old man with a history of obesity, heart failure, pulmonary hypertension, chronic hypoxic respiratory failure on home oxygen, vertebral compression fractures, and type 2 diabetes mellitus presented with worsening dyspnea and signs of volume overload. Physical exam was notable for diffuse muscle wasting, facial plethora, violaceous abdominal striae, and proximal muscle weakness. Workup showed an elevated 24-hour urinary free cortisol (UFC) of 126 µg, an ACTH level of 78.9 pg/mL, and lack of suppression on a 1‑mg overnight dexamethasone suppression test. MRI of the pituitary showed pars intermedia cyst. Inferior petrosal sinus sampling showed maximum left inferior petrosal sinus to peripheral ACTH ratio of 1.34 at baseline and 1.31 post-stimulation. Octreoscan imaging revealed a 1.3-cm right upper-lobe pulmonary nodule with intense radiotracer uptake, consistent with a somatostatin receptor–positive neuroendocrine tumor. He was a high surgical risk candidate for excision and biopsy due to underlying comorbidities. He was started on osilodrostat 2 mg twice daily with dexamethasone 1 mg daily as part of a block and replace strategy in addition to SBRT. Follow-up 24-hour UFC was 13.5 µg/dL, indicating a biochemical response after SBRT and medical management.

Discussion:
Tumors causing ECS can be broadly classified as aggressive, such as small cell carcinoma of bronchus, or more indolent, such as bronchial carcinoids. In cases of aggressive tumors, circulating ACTH and cortisol levels are often extremely high, resulting in pronounced muscle wasting with weakness, hyperpigmentation, and rapid clinical deterioration typically within three to six months. Bronchial carcinoids are often indolent tumors that can cause ECS and require a high index of suspicion to pursue appropriate diagnostic workup. They can develop all of the typical Cushingoid features because of the long duration of hypercortisolemia before clinical presentation and may be biochemically similar to patients with Cushing’s disease. Surgical removal of the tumor is the optimal curative treatment for ECS, but those at high surgical risk have limited therapeutic options. Radiation therapy is not routinely used for treatment of ECS and our case highlights it can be successfully used as an alternative option in high surgical risk patients.

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