Chronic pancreatitis causes pain, maldigestion and weight loss, and, as the disease progresses, diabetes and a set of complications. The features follow from the loss of parenchyma, the functioning tissue of the gland: the same process that destroys the enzyme-producing acinar cells eventually destroys the insulin-producing islet cells as well.
Pain
Pain dominates the early stage of the disease, when a lot of parenchymal tissue is still present. It is mostly felt in the epigastric region and radiates to the back, though its location and intensity vary between patients. It can be intermittent or constant, with pain-free intervals, and over time the pattern usually changes from episodic to continuous. Eating can set the pain off, so patients may eat less to avoid it and lose weight as a result.
Pain does not correlate with the severity of the pancreatic damage. Some patients have imaging findings of extensive necrosis while they are still pain-free, and pain often lessens late in the disease, as inflammation and glandular tissue are lost.
Maldigestion and weight loss
The underlying problem is exocrine pancreatic insufficiency: the pancreas no longer makes enough enzymes to digest food. It becomes evident only when more than 80% of the exocrine gland is destroyed, which is why early disease is easy to miss; by the time it is overt, steatorrhea is present.
Steatorrhea is the passage of light-coloured, foul-smelling faeces. It is caused by maldigestion: the failing gland no longer delivers enough digestive enzymes to break down fat, and the unabsorbed fat leaves in the stool. The malabsorption leads to malnutrition, and fat-soluble vitamin deficiency is common.
Diabetes
Diabetes mellitus follows the loss of islet cells, and its lifetime prevalence in chronic pancreatitis is more than 80%. It is driven by loss of insulin secretion rather than by insulin resistance, but the complications of diabetes in these patients, such as organ damage like neuropathy, are not that common.
Bone disease and vascular complications
Osteoporosis and osteopenia develop because the malabsorption of vitamin D and calcium weakens bone. About 65% of patients with chronic pancreatitis have a metabolic bone disorder such as osteopenia or osteoporosis, related largely to vitamin D deficiency.
Splenic vein thrombosis, a clot in the splenic vein, can lead to portal vein hypertension and consequent bleeding in the gastrointestinal tract.
Long-term cancer risk
Pancreatic cancer is an additional long-term risk of chronic pancreatitis.
These features describe chronic pancreatitis in general. One subtype, autoimmune pancreatitis, has its own histology and presentation and responds dramatically to steroids.