Our Team

Alexandra Guillaume, MDAlexandra Guillaume, MD

Director, Gastrointestinal Motility Center, and Assistant Professor, Department of Medicine

Dr. Guillaume is a board-certified gastroenterologist with expertise in motility disorders of the gastrointestinal tract. She leads the Stony Brook University Hospital Gastrointestinal Motility Center which specializes in the diagnosis and management of feeding and swallowing disorders as well as luminal motility disorders involving diarrhea and/or constipation, refractory GERD, irritable bowel syndrome and small intestinal bacterial overgrowth. Under the leadership of Dr. Guillaume, the motility center provides high resolution esophageal and anorectal manometry, esophageal pH testing, hydrogen breath tests, as well as Smart Pill.

Dr. Guillaume graduated from the Tufts University School of Medicine. She then completed Internal Medicine residency at New York University Medical Center prior to joining the GI fellowship program at Stony Brook University Hospital. She also has additional fellowship training in the management of enteral and parenteral nutrition from NY Presbyterian Hospital - Columbia University Medical Center.

Lionel S. D’Souza, MDLionel S. D’Souza, MD

Director, Endoscopic Surgery

Dr. D’Souza is an Assistant Professor of Medicine, Division of Gastroenterology and Hepatology at Renaissance School of Medicine. He is a member of the Advanced Diagnostic and Therapeutic Endoscopy team at Stony Brook University Hospital with expertise in pancreatic diseases, biliary tract diseases and malignant and pre-malignant tumors of the gastrointestinal tract. He specializes in endoscopic retrograde cholangiopancreatography (ERCP), diagnostic and therapeutic endoscopic ultrasound (EUS), endoscopic mucosal resection (EMR) and endoluminal stent placement.

Dr. D’Souza has a special interest in advanced minimally invasive endoscopic techniques such as endoscopic submucosal dissection (ESD), peroral endoscopic myotomy (POEM) and endoscopic suturing and their applications in the resection of cancerous and pre-cancerous lesions of the GI tract as well as in the management of achalasia, gastroparesis, obesity and gastroesophageal reflux disease (GERD).