Synonyms: Pancreatic fat necrosis, nodular fat necrosis of pancreatic disease
Etiology: In part, due to cutaneous enzymatic fat necrosis from circulating pancreatic enzymes Associations: Acute and chronic pancreatitis, acinar cell carcinoma Clinical: Erythematous subcutaneous nodules favoring lower extremities, may drain spontaneously; arthritis, serositis, abdominal pain, nausea, vomiting, lytic bone lesions Histology: Subcutaneous fat necrosis with loss of adipocyte nuclei,
"ghost" cells, stippled basophilia of calcification, neutrophils early, mixed infiltrate late Evaluation: Serum amylase, lipase, CBC with differential (eosinophilia correlates with acinar cell carcinoma), pancreatic imaging studies
Treatment: Correct underlying pancreatic disease Prognosis: Usually poor in carcinoma-associated disease because of advanced disease, and variable in pancreatitis-associated, depending upon severity of underlying disease
Pancreatic panniculitis is a form of subcutaneous fat necrosis that occurs as a rare manifestation of various pancreatic diseases, most commonly pancreatitis, or pancreatic carcinoma. Fat necrosis at remote sites occurs in only a small percentage of those with pancreatic disease. Its pathogenesis is uncertain. A review of 893 hospital admissions for various pancreatic diseases revealed only three cases of pancreatic panniculitis (1). Circulating pancreatic enzymes, lipase and amylase, are elevated in most but not all cases of pancreatic pannicu-litis (2). Human pancreatic lipase has been identified in lesions of pancreatic panniculitis, supporting its role in the pathogenesis of the disease (3). In vitro and clinical observations suggest that factors other than circulating amylase and lipase are necessary for the development of pancreatic panniculitis. In vitro incubation of human adipose tissue with pancreatic enzymes and serum from a patient with pancreatic panniculitis and elevated enzymes failed to induce fat necrosis, suggesting that there are other local factors or a labile circulating factor needed to induce the necrosis (4). Clinical observations indicate that pancreatic panniculitis occurs in only a small number of patients with pancreatic disease. It does not develop in many with striking elevation of pancreatic enzymes, and may arise in patients with normal circulating enzymes. Lesions of pancreatic panniculitis have been induced at sites of injury from a vascular procedure, suggesting that local trauma in a susceptible individual is capable of inducing disease (5). Localized lesions have also been induced by paracentesis in a patient with acute pancreatitis, most likely the direct effect of peritoneal pancreatic enzymes on subcutaneous fat reached via the needle tract from the procedure (6).
Most cases of pancreatic panniculitis occur in association with acute and chronic pancreatitis, and pancreatic adenocarcinoma. Most of the pancreatitis-associated cases are due to chronic alcoholism, but some are due to cholecystitis with biliary tract obstruction and trauma. Malignancy-induced pancreatic panniculitis is almost always due to acinar cell carcinoma. Although this tumor accounts for fewer than 5% of pancreatic malignant neoplasms, it produces large quantities of lipase and other digestive enzymes, likely accounting for the association (7). Other triggers of pancreatic panniculitis include pancreatic pseudocyst, post-traumatic pancreatitis (8), and structural anomalies such as pancreas di visum (9).
Patients who develop pancreatic panniculitis present with erythematous to brown, usually painful, subcutaneous nodules (Figure 21.1). The most common site of involvement is pretibial, but lesions may involve the upper extremities and trunk, and may spare the legs. Nodules are indurated, and many have some softening or fluctuation in the central portion, indicating liquefactive necrosis. In some patients, spontaneous ulceration occurs, with drainage of creamy or brown viscous fluid, representing degenerated adipose tissue. Spontaneous involution with lipoatrophy and dyspigmentation occurs in several weeks, and may or may not correlate with improvement of the underlying disease. Paradoxically, pancreatic panniculitis associated with alcoholic pancreatitis and markedly ele-
vated pancreatic enzymes tends to have more localized cutaneous disease with less likelihood of spontaneous rupture, drainage, and ulceration than that associated with pancreatic carcinoma (8).
Many presentations of pancreatic panniculitis appear to represent localized disease, but others have numerous systemic manifestations, including those directly associated with pancreatitis such as abdominal pain, nausea, vomiting, chest pain, jaundice, and fever. Approximately 40% of pancreatitis-associated cases and 90% of malignancy-associated cases present without abdominal pain, nausea, or vomiting. Peripheral eosinophilia may occur, and is far more likely to be associated with underlying carcinoma than pancreatitis (10). Arthritis, described in approximately 60% of cases, usually represents periar-ticular fat necrosis. In some instances, the fat necrosis extends into the joint space resulting in a true arthritis. The most commonly affected joints are ankles, fingers, knees, and elbows (1). Ascites, pleural, and pericardial effusions may also occur (11). In one case with polyserositis, the presence of pleural deposition of IgG and C3 and reduced levels of hemolytic complement in blood, pleural, and pericardial fluid were detected, suggesting immunemediated injury (11). Lytic bone lesions due to medullary fat necrosis have also been described. These may be mistaken for metastatic disease in malignancy-associated cases (12).
Pancreatic panniculitis may be the presenting sign of previously undiagnosed pancreatic disease. The clinical presentation of subcutaneous nodules with arthritis and serositis is not specific, but may suggest connective tissue disease accompanied by erythema nodosum. Pancreatic panniculitis is one of several disparate entities that may resemble erythema nodosum, but is readily distinguished from it based upon histologic features (Figure 21.2A and 21.2B). The epidermis and dermis are usually normal. The subcutaneous tissue has extensive fat necrosis with loss of adipocyte nuclei. Retained cell borders form "ghost-like" fat cells. There is stippled basophilia caused by calcification, and a mixed inflammatory cell infiltrate varying with the age of the lesion. Neutrophils predominate early (13). A septal pattern of inflammation has been described in an early lesion (14).
Most cases of pancreatic panniculitis wax and wane. The only effective treatment are to correct the underlying disease, tumor resection for localized malignancy, bowel rest and supportive measures for pancreatitis, or surgical correction of developmental anomalies or mechanical obstruction. This disease is important to recognize because it may closely mimic erythema nodosum, a common cause of panniculitis. A distinctive histologic pattern in pancreatic panniculitis is a valuable clue to the recognition of serious previously undiagnosed pancreatic disease.
Figure 21.2. (A and B) Multifocal fat necrosis with "ghost cell" formation, neutrophils, and stippled calcification.
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