What are the latest advances in the diagnosis of autoimmune bullous dermatoses?

By Sylvia Hsu, MD, February 1, 2021

In this month’s Clinical Applications column, DermWorld Editorial Advisory Workgroup member Sylvia Hsu, MD, talks with Kiran Motaparthi, MD, about his Clinics in Dermatology paper, ‘Advances in the diagnosis of autoimmune bullous dermatoses.’

DermWorld: If a patient has only erosions in the mouth and I’m worried about erosive lichen planus versus pemphigus vulgaris (PV) versus cicatricial pemphigoid, where do I begin? Should I biopsy the inside of the mouth for histopathology and DIF or are there more sensitive and specific blood tests now?

Dr. Motaparthi: If the clinician has a strong suspicion for PV, then a reasonable approach is to initially obtain enzyme-linked immunosorbent assay (ELISA) for anti-Dsg3 antibodies. ELISA for anti-Dsg3 antibodies is the most accurate diagnostic method for PV and is, therefore, a highly useful and non-invasive test in this context. However, if the differential diagnosis is broad or uncertain or if ELISA for anti-Dsg3 is negative, then biopsies for histopathology and DIF should be obtained. Although autoantibodies against NC16a, LAD-1, laminin 332, β4 integrin or COL7 may be identified, the C-terminus of BP180 is the most common antigenic target in MMP. While ELISA for anti-BP180-NC16a antibodies is accessible, ELISA for autoantibodies directed against the C-terminus of BP180 is not currently commercially available. Additionally, circulating autoantibodies are undetectable by IIF in a significant number of patients with MMP. In LP, there are no circulating autoantibodies. Therefore, diagnostic confirmation of MMP and LP relies upon characteristic DIF patterns. For MMP and PV, biopsies for DIF should be taken from normal mucosa adjacent to an erosion or Nikolsky sign; for LP, biopsy for DIF should represent partly lesional and partly normal mucosa.

DermWorld: Which ELISA tests are commercially available? Which labs perform these tests? What is the cost?

Dr. Motaparthi: ELISA is available to detect circulating autoantibodies directed against Dsg1, Dsg3, envoplakin and periplakin, BP180-NC16a, BP230, COL7, eTG, and tTG. Availability of each ELISA varies, but these tests are generally available through several academic centers and commercial laboratories. ELISA is cost effective, with each assay typically under $20, although insurance coverage may vary. ELISAs for circulating autoantibodies against less commonly sought antigenic targets such as Dsc1, Dsc3, laminin 332, and p200 may be available through select academic centers or for research.

DermWorld: Are there any autoimmune bullous diseases in which an ELISA should be the gold standard in establishing the diagnosis?

Dr. Motaparthi: ELISA is the most accurate confirmatory diagnostic test for PV and pemphigus foliaceus (PF). Based on meta-analysis, the accuracy of ELISAs for anti-Dsg1 and anti-Dsg3 is 97.5%. The cost-effectiveness and specificity of ELISA exceeds that of routine histopathology and DIF in the diagnosis of PV and PF. While immunoblot for envoplakin or periplakin is considered the gold standard diagnostic method for PNP, ELISA for autoantibodies directed against these plakin family proteins is as accurate as immunoblot. The sensitivity of these methods exceeds that of IIF on rat bladders, the classic combined acantholytic and interface tissue reaction pattern, and the classic combined intercellular and junctional DIF pattern. DIF remains the diagnostic method of choice for subepithelial blistering disorders including BP, GP, and EBA. DIF is also the most accurate initial diagnostic method for the IgA-mediated bullous dermatoses, although ELISA for anti-eTG is highly specific for DH. There is an important caveat to the use of ELISA for diagnosis. First, pre-test probability should be considered. If diagnostic suspicion is high for a singular blistering disorder (such as PV), then ELISA is reasonable. However, if the differential diagnosis is broad or if there is uncertainty of an autoimmune blistering disorder, then DIF is the best next step.

DermWorld: If I suspect a patient has dermatitis herpetiformis, but the patient is already on a gluten-free diet, what test can I do to confirm the diagnosis?

Dr. Motaparthi: While IgA class anti-eTG and anti-tTG antibodies can both be detected in patients with DH, only anti-eTG antibodies are specific for DH. Anti-tTG antibodies are also detected in patients with celiac disease without DH, and their quantity decreases in the context of a gluten-free diet. Therefore, ELISA for anti-eTG can be used to confirm the diagnosis of DH in a patient who is adherent to gluten-free diet. Direct immunofluorescence of perilesional skin can also be used to confirm the diagnosis. ELISA for anti-eTG can subsequently be used to monitor disease activity, while ELISA for anti-tTG can be used to monitor dietary adherence. It is important to remember that IIF performed on skin substrate is always negative in DH, given that the target antigen eTG is not present in the dermis of normal skin.

“An upcoming meta-analysis highlights modified criteria for the diagnosis of PNP: Three major criteria and two minor criteria. When all three major criteria or two major and both minor criteria are met, up to 90% of PNP cases are captured.”

─ Kiran Motaparthi, MD

DermWorld: If a patient has cancer and mouth erosions, is that paraneoplastic pemphigus?

Dr. Motaparthi: No. PNP (or paraneoplastic autoimmune multiorgan syndrome) is a very rare autoimmune bullous disorder with variable clinical, histopathologic, and immunopathologic features. An upcoming meta-analysis highlights modified criteria for the diagnosis of PNP: Three major criteria (mucosal erosions with or without cutaneous involvement, associated neoplasm, and evidence of anti-plakin autoimmunity) and two minor criteria (acantholysis and/or interface tissue reaction on histopathology and DIF with intercellular and/or junctional immunoreactant deposition). When all three major criteria or two major and both minor criteria are met, up to 90% of PNP cases are captured. More common explanations for oral erosions should be considered initially, such as chemotherapy-induced mucositis, lichenoid stomatitis including PD-1/PD-L1 eruptions and oral graft-versus-host-disease, herpesvirus infection, and pemphigus vulgaris. Of note, detection of autoantibodies against Dsg3 in this context does not distinguish between PV and PNP, since patients with PNP may also have antiDsg3 autoantibodies. Instead, ELISA or immunoblot for antibodies directed against envoplakin and/or periplakin or IIF on transitional epithelium permit distinction between these two disorders.

Dr. Motaparthi is a dermatologist at University of Florida College of Medicine. His paper appeared in Clinics in Dermatology. Dr. Motaparthi has no relevant financial or commercial conflicts of interest.

Disclaimer: The views and opinions expressed in this article do not necessarily reflect those of DermWorld.

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