Because of its clinical polymorphism MC syndrome may overlap with a variety of immunolog-ical and neoplastic diseases; namely, other systemic vasculitides, Sjogren's syndrome, autoimmune hepatitis, and B-cell lymphoproliferative disorders.
Differential diagnosis with other systemic vasculitides is quite easy if serological markers (cry-oglobulinemia, specific autoantibodies, and complement profile) and histopathological patterns (different alterations and size of involved vessels) are correctly evaluated. MC and Sjogren's syndrome may share various symptoms: xerostomia, xerophthalmia, arthralgias, purpura, serum cryoglobulins and rheumatoid factor, as well as the possible development of B-cell lymphomas (Vitali et al., 2002; Ramos-Casals et al., 2001). A correct diagnosis can be done in the majority of cases by considering the following findings: typical histo-pathological alterations of salivary glands and specific autoantibodies (anti-RoSSA/LaSSB) of Sjogren's syndrome (Vitali et al., 2002) are rarely found in MC patients; conversely, HCV infection, cutaneous leukocytoclastic vasculitis, and renal and/or liver involvement are seldom recorded in primary Sjogren's syndrome. However, in some patients the differential diagnosis may result very difficult; thereafter, it might be correct to classify these cases as MC/Sjogren's overlap syndrome.
Patients with autoimmune hepatitis may present low amounts of serum cryoglobulins, HCV-positivity, and some extrahepatic manifestations, such as thyroiditis, sicca syndrome, and arthritis (Lenzi et al., 1991; Ferri et al., 1994). In these instances, searching some patognomonic findings can do a correct classification of the disease; in particular, high titre autoantibodies (ANA, ASMA, and anti-LKMl) are more often detectable in autoimmune hepatitis, while leukocyto-clastic vasculitis and complications such as membranoproliferative glomerulonephritis are typically found in MC patients (Ferri et al., 2004).
Finally, B-NHL complicating HCV-related MC can be confused with some 'idiopathic' B-NHL showing clinico-serological findings of MC. The differential diagnosis of these two entities may be important especially for its therapeutic implications: the treatment of B-cell NHL complicating the MC may need some precautions due the concomitance of HCV infection and the possible liver and/or renal failure. These complications should also be taken into account in HCV-related B-NHL without MC syndrome (Ferri et al., 2000).
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