Don't miss it: a rare case of multifocal necrotizing fasciitis

lution of liver dysfunction and was commenced on glucocorticoid therapy to manage residual IgG4 disease with good clinical progress and no further complications. Strictures of the hepatic hilum can pose a diagnostic difficulty. This case highlights IgG4-related sclerosing cholangitis (IgG4-SC), an extra-pancreatic manifestation of IgG4-related sclerosing disease (IRSD), as a differential for benign hepatic strictures. Hilar or intrahepatic ductal involvement, together with an associated softtissue mass in IgG4-SC presentation, can mimic hilar CCa presentation. Radical surgery for suspected CCa is considered the only option to prolong survival despite the associated post-operative morbidity. The vast majority of IgG4-SC cases are managed surgically for suspected biliary malignancy when there is no evidence of pancreatitis. Diagnosis of IgG4-SC has been aided by the development of HISORt (histology, imaging, serology, other organ involvement and response to therapy) criteria and Japanese IgG4-SC working group statement allowing for distinction from CCa. IRSD is characterized by tumefactive lesions, a dense lymphoplasmacytic infiltrate rich in IgG4-positive plasma cells and storiform fibrosis. Clinical symptomatology on presentation includes obstructive jaundice, weight loss, mild to moderate abdominal pain, steatorrhoea and new onset diabetes. Radiological features include diffuse or segmental narrowing of the intrahepatic and/or extrahepatic bile duct associated with bile duct wall thickening. Although the utility of elevated serum IgG4 concentrations (>140 g/L) can be highly suggestive of IgG4-SC, it is not regarded pathognomonic as approximately 30% of patients have normal serum IgG4 concentrations. Other sensitive but not specific serological markers include hypergammaglobulinaemia, hyper IgG, antinuclear antibody, rheumatoid factor and peripheral eosinophilia. While co-presentation with autoimmune pancreatitis commonly occurs, IgG4-SC can occur as isolated biliary disease and can manifest as either a diffuse sclerosing cholangitis or a hilar pseudotumourous mass. Enlargement of the salivary or lacrimal gland, retroperitoneal fibrosis or renal lesion may also be noted on presentation. Given the unreliability of imaging modalities and brush cytology in distinguishing hepatic strictures, preoperative histological analysis is desired, through either Vater’s ampulla biopsy, liver needle biopsy or bile duct biopsy, with more than 10 IgG4-positive plasma cells used as the diagnostic threshold. Glucocorticoids are typically the first line of therapy, with most patients demonstrating a response within 4 weeks and treatment tapered over 3–6 months. This response is dependent on the degree of fibrosis within the affected organs, and monitored with a decline in serum biochemical markers and radiological improvement. Alternate treatment regimen includes the use of steroid sparing agents following steroid-induced remission and rituximab in patients with recurrent or refractory disease. In conclusion, this case highlights an extra-pancreatic manifestation of IgG4-related sclerosing disease and illustrates the diagnostic challenges faced in differentiating between benign and malignant biliary strictures.