Meet the Providers

Dr. Wilson Jackson, MD, FACP, FACG, AGAF

Dr. Wilson Jackson received his undergraduate degree from Bowdoin College cum laude in English literature and his Doctor of Medicine degree from Northwestern University in Chicago. He completed a residency in internal medicine at Northwestern Memorial Hospital and a fellowship in gastroenterology and hepatology at Thomas Jefferson University in Philadelphia. Training in advanced therapeutic endoscopy was completed at Temple University Hospital. He was a faculty member at Temple University Medical Center, where he was an assistant professor in the Division of Gastroenterology before moving to the Harrisburg area.

Dr. Jackson is board certified in internal medicine and gastroenterology. He was elected a fellow of the American Gastroenterology Association, American College of Physicians, and American College of Gastroenterology. He is also a member of the Pennsylvania Medical Society, American Medical Association, American Society of Gastrointestinal Endoscopy and Pennsylvania Society of Gastroenterology. He has also served as president of the latter.

Dr. Jackson has served on the National Affairs Committee for the American College of Gastroenterology. He has presented several papers at national medical meetings, and has written chapters for medical textbooks.

Dr. Steven P. Siegelbaum, MD, FACG

Dr. Steven P. Siegelbaum received his undergraduate degree in psychology from New York University and his Doctor of Medicine degree from University of Medicine and Dentistry of New Jersey. He completed his internal medicine residency and fellowship in gastroenterology from the State University of New York, Upstate Medical Center, in Syracuse, New York. He moved to Harrisburg and started the practice of Siegelbaum, Gunder and Lacey in 1980.

Dr. Siegelbaum is board certified in internal medicine and gastroenterology. He is a member of the American College of Gastroenterology, American Gastroenterology Association, American Society for Gastrointestinal Endoscopy, Pennsylvania Society of Gastroenterology, Central Pennsylvania Society for Gastrointestinal Endoscopy and the American Medical Association. Dr. Siegelbaum is active in the PinnacleHealth System. He is a current member of the Board of Directors for the PinnacleHealth System and a former president of the PinnacleHealth Medical Staff. His interests in gastroenterology include inflammatory bowel disease and colon cancer screening and prevention.

Dr. Paul G. Lacey, MD, FACP, FACG

Dr. Paul Lacey received his undergraduate degree from Villanova University, graduating magna cum laude in biology. He received his Doctor of Medicine degree from Pennsylvania State University in Hershey, PA. He completed his internal medicine residency at the University of Virginia in Charlottesville, VA. His gastroenterology and hepatology fellowship was completed at Pennsylvania State University, where he later served as a clinical instructor.

Dr. Lacey is board certified in internal medicine and gastroenterology. He is a member of the American Gastroenterology Association, American College of Gastroenterology, American College of Physicians and Pennsylvania Society of Gastroenterology. Dr. Lacey has presented research at national meetings and participates in the continuing medical education program. He recently completed a 10 year board recertification in internal medicine and gastroenterology. Dr. Lacey and his family have lived in central Pennsylvania for more than 20 years. He is a staff member at the PinnacleHealth System and Holy Spirit Hospital.

Dr. John J. Michel, DO

Dr. John Michel received his undergraduate degree in pharmacy from Ohio Northern University and his Doctor of Osteopathy degree from Philadelphia College of Osteopathic Medicine in Philadelphia, PA. He completed his internal medicine residency at Philadelphia College of Medicine, where he was chief internal medicine resident his last year. He completed a fellowship in gastroenterology and hepatology at the University of Medicine and Dentistry of New Jersey with rotation at Hackensack University, University Hospital, East Orange Veterans Administration Hospital and Liver Institute of Newark, New Jersey. He was chief gastroenterology fellow his last year of training before moving to the Harrisburg area.

Dr. Michel is board certified in internal medicine, gastroenterology and hepatology. He is a member of the American Gastroenterology Association, American Society of Gastrointestinal Endoscopy, American Medical Association, American Osteopathic Association, American Osteopathic Board of Internal Medicine, Central Pennsylvania Society for Gastrointestinal Endoscopy, Pennsylvania Society of Gastroenterology and the American College of Gastroenterology.

Dr. Michel is active on the staff at Holy Spirit Hospital and the PinnacleHealth System. His areas of special interest include inflammatory bowel disease and liver disease.

Dr. David S. Mize, M.D.

Dr. David Mize received his undergraduate degree from the University of California, Davis, in electrical engineering. He went on to receive a Master of Science degree from the University of California, San Diego, in bioengineering. He received his Doctor of Medicine degree from Hahnemann University School of Medicine and completed his internal medicine residency at Dartmouth-Hitchcock Medical Center in Lebanon, NH. He then served as chief resident of internal medicine at Penn State Milton S. Hershey Medical Center before completing a fellowship in gastroenterology and hepatology there. He joined Jackson Siegelbaum Gastroenterology in 2004.

Dr. Mize is board certified in internal medicine, gastroenterology and hepatology. He is a member of the American College of Gastroenterology, American Gastroenterology Association, American Society for Gastroenterology, Pennsylvania Society of Gastroenterology and the American College of Physicians.

Dr. Mize has presented research at national meetings, published papers and has written a textbook chapter.

Dr. Adnan Ahmad, DO

Dr. Adnan Ahmad received his undergraduate degree in biology from Rutgers University. He received his Doctor of Medicine degree from the University of Medicine and Dentistry of New Jersey. He completed his internal medicine residency at the University of Connecticut. His gastroenterology and hepatology fellowship was completed at Penn State Milton S. Hershey Medical Center. He joined Jackson Siegelbaum Gastroenterology in 2007.

Dr. Ahmad is board certified in internal medicine, gastroenterology and hepatology. He is a member of the American Gastroenterology Association, American College of Gastroenterology, American Society for Gastrointestinal Endoscopy, Central Pennsylvania Society for Gastrointestinal Endoscopy and Pennsylvania Society of Gastroenterology. He has presented several papers at national medical meetings. He is currently an active staff member of Holy Spirit Hospital and the PinnacleHealth System. His special interests in gastroenterology include inflammatory bowel disease, liver disease, colon cancer and gastroesophageal reflux disease.

Tina M. Navitsky, CRNP

Tina Navitsky, CRNP, received her undergraduate education at York College. She earned her master’s degree in family health at Widener University. She has more than 13 years of nursing experience in intensive care, coronary care, labor and delivery, home health, pediatric oncology and the operating room. She has experience in gastroenterology involving office nursing and endoscopy since 1990.

Ms. Navitsky is board certified as a family nurse practitioner. She is a member of the American Academy of Nurse Practitioners, Central PA Chapter of Nurse Practitioners and Sigma Theta Tau International Society.

Her area of special interest is liver disease, especially hepatitis C. She is a frequent speaker to health care groups on this topic.

Deborah B. Matisse, MSN, CRNP

Deborah Matisse, CRNP, graduated summa cum laude from Hartwick College and was recognized as a faculty scholar. She later received her advanced CRNP degree from Widener University in 2005. She is also a certified lactation consultant. She previously worked as a nurse for Mechanicsburg Area School District and Messiah College and later in a drug addiction clinic. The mother of four, she has remained active in the community as a soccer coach and youth group leader.

Lisa Stokes, CRNP

Lisa Stokes, CRNP, graduated in 1987 with a Bachelor of Science degree in nursing from the University of Pennsylvania. She subsequently received her Master of Science in nursing from the University of Pennsylvania in 1989. She also holds a Bachelor of Fine Arts degree from Kutztown University. She has been a nurse practitioner for more than 16 years. She previously was employed at Mechanicsburg Family Practice and the Penn State University Physicians Group in Middletown. She has worked in gastroenterology since 2001.

Ms. Stokes is board certified by the American Nurses Credentialing Center and is a member of Nurse Practitioners of Central Pennsylvania. She is married with three children and several pets.