Marked Variation in Serum Chromogranin A Levels in a Patient on Chronic Omeprazole Therapy

Abstract

Serum chromogranin A (CgA) is used as a standard marker in the diagnosis of neuroendocrine tumors. We report a case with wide fluctuation (more than 10-fold) in serum CgA levels in a patient on chronic omeprazole therapy. A 67-year-old woman with hypothyroidism presented for evaluation of facial flushing for 1 year. Flushing had increased in intensity over the past several months without any provocative factors. She denied any diarrhea, wheezing, headache, palpitations or facial erythema. Her home medications were aspirin, omeprazole, levothyroxine, and raloxifene. The patient reported no improvement in flushing on stopping raloxifene. Physical exam was unremarkable. On blood testing, she was noted to have mildly elevated serum CgA of 18.8 ng/mL (range 1.9 - 15 ng/mL). Other endocrine tests including serum tryptase, 24-hour urine N-methylhistamine, 24-hour urine 5-hydroxyindoleacetic acid, metanephrines, catecholamines, and serum calcitonin were unremarkable. Serum CgA was repeated because of her continued symptoms. Repeat blood test showed markedly increased CgA value (128 ng/mL). She underwent a CT chest/abdomen/pelvis and octreotide scan. The octreotide scan showed uptake in the right axillary and subcarinal regions. She subsequently underwent endoscopic bronchial ultrasound and mediastinal biopsy of two lymph nodes. Biopsy was negative for any pathological process. PET scan was done to rule out occult malignancies and was negative. Echocardiogram was normal. She was also seen by neurology with unremarkable workup. CgA levels were repeated over a course of three months and levels varied from 126 to 182 ng/mL. She was asked to hold omeprazole for 2 weeks and CgA levels dropped to 24 ng/mL. The patient resumed omeprazole due to worsening reflux. Repeat CgA level three months later on omeprazole was 18 ng/mL. Venlafaxine and paroxetine were tried for flushing but she could not tolerate these due to side effects. It had been previously established that medications which stimulate neuroendocrine cells, in particular proton pump inhibitors (PPI) could lead to falsely elevated CgA levels. The interesting aspect in this case is increase in CgA more than 10-fold and the marked variation in CgA levels while on omeprazole (18 - 182 ng/mL). There is marked variability in serum CgA levels in presence of a PPI as seen in our case. Clinicians should consider repeat testing of CgA levels in setting of abnormal values and also consider stopping contributing medications before testing and making important clinical decisions.




J Med Cases. 2015;6(5):232-234
doi: http://dx.doi.org/10.14740/jmc2135w