Chronic pancreatitis

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Chapter 12 CHRONIC PANCREATITIS

• Chronic pancreatitis, chronic inflammation of the pancreas, is characterised by progressive irreversible loss of pancreatic exocrine and endocrine function.

• Chronic pancreatits manifests with chronic abdominal pain, maldigestion and secondary diabetes mellitus.

• The most common cause in Western nations is alcohol abuse.

• Autoimmune pancreatitis can present as a mass masquerading as a pancreatic malignancy.

AETIOLOGY AND PATHOGENESIS

The most common cause of chronic pancreatitis in Western nations is alcohol abuse (Table 12.1).

TABLE 12.1 Causes of chronic pancreatitis

• Chronic alcohol abuse

• Hypercalcaemia

• Hypertriglyceridaemia

• Cystic fibrosis

• Tropical pancreatitis

• Obstruction, e.g. pancreas divisum, tumour, calculi

Alcohol

Alcohol accounts for 70%–90% of all cases of chronic pancreatitis in Western societies. The onset of alcoholic pancreatitis usually occurs in the fourth decade, and the majority of patients are males consuming alcohol in the order of 100–150 g/day (i.e. 10–15 standard drinks/day) in the 5–15 years prior to initial presentation. Typically, the initial clinical presentation of alcohol-mediated pancreatic injury is acute pancreatitis. However, the characteristic histological and radiological features of chronicity (atrophy, fibrosis and calcification) are already evident in a large proportion of these patients on initial presentation.

Idiopathic chronic pancreatitis

This condition has a bimodal distribution with an earlier median peak at 19 years and a late median peak at 56 years of age. This condition also presents initially as clinical recurrent acute pancreatitis manifesting chronic features over time. Several genetic defects have been linked to the development of idiopathic chronic pancreatitis. A less severe phenotype of idiopathic chronic pancreatitis in the absence of the classic full cystic fibrosis syndrome can be caused by mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene on chromosome 7q31.2. Inappropriate activation of the cationic trypsinogen gene (PRSS1), and mutations of the serine protease inhibitor Kazal type 1 (SPINK1), a potent natural inhibitor of pancreatic trypsin activity, may also result in chronic pancreatitis.

Hereditary pancreatitis

This inherited form of pancreatitis caused by mutations of the cationic trypsinogen gene (PRSS1) on chromosome 7q35 is autosomal dominant with 80% penetrance. Trypsin activation is central to the activation of the other digestive pancreatic proenzymes. The onset of this condition is in childhood, with progression to chronic pancreatitis as early as the late teens. There is an increased risk of pancreatic cancer: 40% of patients will have cancer by age 70. Mutation of the SPINK1 gene has been implicated in hereditary pancreatitis. Other inherited disorders that may cause pancreatitis are cystic fibrosis (see below), familial hyperparathyroidism with hypercalcaemia, familial hyperlipidaemia due to lipoprotein lipase deficiency and apolipoprotein C-II deficiency.

Cystic fibrosis

There is a correlation between the degree of abnormal CFTR function and severity of cystic fibrosis. Exocrine pancreatic insufficiency occurs in approximately 85% of patients with cystic fibrosis due to defective secretory capacity of bicarbonate and digestive enzymes. Chronic pancreatitis and pancreatic atrophy arises from inspissated protein-rich acinar secretions that obstruct the ducts resulting in cellular destruction and fibrosis.

Tropical pancreatitis

This form of pancreatitis is restricted to areas within 30 degrees of latitude from the equator and is associated with protein–calorie malnutrition. The pathogenesis of this condition has not been clarified.

Autoimmune pancreatitis

Autoimmune pancreatitis is characterised by the presence of autoantibodies and elevated immunoglobulins (elevated IgG4) in the serum, and lymphocytic infiltration of the pancreas. It may masquerade as pancreatitis or as a pancreatic mass mistaken for cancer. Corticosteroids are the mainstay of therapy for this condition.

Obstructive pancreatitis

Obstruction of the pancreatic duct by tumours, papillary stenosis, cysts and strictures may cause pancreatitis. In pancreas divisum, the dorsal pancreatic duct is drained by the minor papilla. Inadequacy of drainage may, in a small minority of cases of pancreas divisum, result in acute or chronic pancreatitis.

ASSESSMENT

The diagnosis of chronic pancreatitis is clinical, based on symptomatology, known risk factors and investigatory evidence.

History and examination

Abdominal pain

Abdominal pain can be variable with this condition and can range from mild discomfort to intractable severe pain associated with narcotic dependence. The pain is localised to the upper abdomen and radiates to the back. The pain may occur postprandially and may be relieved by leaning forwards. Chronic constant abdominal pain eventually develops in up to 80% of patients. A proportion of patients with chronic pancreatitis do achieve pain relief on entering a ‘burnout phase’ coinciding with the onset of pancreatic insufficiency and pancreatic calcification.

Steatorrhoea and diarrhoea

Pancreatic exocrine insufficiency may occur as early as 5–6 years after disease onset. Maldigestion may occasionally occur in the absence of abdominal pain. Steatorrhoea occurs in approximately 30% of patients with chronic pancreatitis, and a history of the passage of ‘oil’ at defecation is virtually pathognomonic of pancreatic steatorrhoea. The degree of steatorrhoea depends on the amount of fat ingested.

Weight loss

Weight loss may be marked and can be related to a number of factors (e.g. malabsorption, inadequate diet). Protein–calorie malnutrition is common.

Diabetes mellitus

Impaired glucose tolerance and secondary diabetes mellitus occur in up to 50% of patients with chronic pancreatitis.

Social sequelae

Social sequelae of chronic alcohol abuse often associated with chronic pancreatitis include unemployment and narcotic addiction.

Investigations

Serum pancreatic enzymes

The diagnosis of acute pancreatitis is made clinically and confirmed by an elevated serum amylase and/or lipase greater than three times the upper limit of normal. However, in chronic pancreatitis, the levels of these enzymes may be normal or below the normal range.

Pancreatic imaging

Abdominal X-ray, ultrasonography

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