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      Drugs & Diseases > Dermatology

      Bullous Pemphigoid Workup

      Updated: Oct 14, 2020
      • Author: Lawrence S Chan, MD; Chief Editor: Dirk M Elston, MD  more...
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      Workup

      Laboratory Studies

      To establish a diagnosis of bullous pemphigoid, the following tests should be performed: histopathologic analysis from the edge of a blister and DIF studies on normal-appearing perilesional skin. [2] If the DIF result is positive, indirect immunofluorescence (IDIF) is performed using the patient's serum. The preferred substrate for IDIF is salt-split normal human skin substrate.

      Direct immunofluorescence studies

      DIF studies demonstrate in vivo deposits of antibodies and other immunoreactants, such as complement. DIF tests usually demonstrate IgG (70-90% of patients) and complement C3 deposition (90-100% of patients) in a linear band at the dermal-epidermal junction. This pattern of immunoreactants is not specific for bullous pemphigoid and may be seen in cicatricial pemphigoid and epidermolysis bullosa acquisita. Bullous pemphigoid can be differentiated from these conditions by incubating the patient's skin biopsy sample in 1 mol/L salt prior to performing the DIF technique. This process induces cleavage through the lamina lucida. DIF on salt-split skin reveals IgG on the blister roof (epidermal side of split skin) in patients with bullous pemphigoid, while, in CP and EBA, the IgG localizes to the blister floor (dermal side of split skin).

      The optimal location for DIF testing is normal-appearing perilesional skin. False-positive results can be observed when it is performed on lesional skin. There is a significant false-negative rate if the skin biopsy specimen is taken from skin of the legs. [3]  Rarely, skin biopsy samples placed in transport media may yield false-negative results. This observation makes the use of fresh tissue the preferred substrate for DIF studies. See the image below.

      Direct immunofluorescence study performed on a per Direct immunofluorescence study performed on a perilesional skin biopsy specimen from a patient with bullous pemphigoid detects a linear band of immunoglobulin G deposit along the dermoepidermal junction.
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      Indirect immunofluorescence

      IDIF studies document the presence of IgG circulating autoantibodies in the patient's serum that target the skin basement membrane component. Seventy percent of patients with bullous pemphigoid have circulating autoantibodies that bind to split skin. The titer of circulating antibody is not correlated with the disease course.

      IDIF studies can be used to detect the patient's IgG circulating autoantibodies that bind to the epidermal roof (upper part) of the salt-split skin substrate. See the image below.

      Indirect immunofluorescence study performed on sal Indirect immunofluorescence study performed on salt-split normal human skin substrate with the serum from a patient with bullous pemphigoid detects immunoglobulin G class circulating autoantibodies that bind to the epidermal (roof) side of the skin basement membrane.
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      Other Tests

      Experimental procedures available in research laboratories include direct and indirect immunoelectron microscopy, immunoblotting, immunoprecipitation, and enzyme-linked immunosorbent assay (ELISA), as follows:

      • Direct and indirect immunoelectron microscopy: Direct and indirect immunoelectron microscopy (immunoEM) ultrastructurally localize in vivo–bound IgG autoantibodies (direct immunoEM) or the binding site of circulating IgG autoantibodies (indirect immunoEM) at the basement membrane. IgG autoantibodies are detected at the hemidesmosome/upper lamina lucida areas of the skin basement membrane.

      • Immunoblotting [60] : Immunoblotting or Western blotting demonstrates reactivity of IgG in the sera of patients with proteins extracted from healthy human skin. The sensitivity of immunoblotting varies. In 75% of patients, a reaction occurs with the BP230 antigen, while, in 50% of patients, a reaction occurs with the BP180 antigen.

      • Immunoprecipitation: Like immunoblotting, immunoprecipitation demonstrates reactivity with BP230 and BP180. Unlike immunoblotting, immunoprecipitation is performed with native, rather than denatured, protein and is more sensitive. Immunoprecipitation is more difficult to perform and generally less available than immunoblotting. In most cases, immunoprecipitation detects autoantibodies specific for BP230 and BP180.

      • Enzyme-linked immunosorbent assay: The ELISA technique analyzes the bullous pemphigoid antigen-specific IgG autoantibodies in the patients' sera by using various lengths of recombinant proteins of the BPAg1 or BPAg2 antigens. In several reports, ELISA has been demonstrated to be highly sensitive and specific. [61] ELISA kits for testing bullous pemphigoid antigen-specific IgG autoantibodies are now available commercially. However, only a few medical centers currently offer this service. ELISAs based on recombinant proteins encoded by BP230 and BP180 have been developed. [62] These assays are not commercially available, but they offer promise as investigational tools. An ELISA based on BP180 demonstrates sera reactivity with more than 90% of patients with bullous pemphigoid.

      • Immunohistochemistry: If freshly frozen tissue is not available for direct immunofluorescence microscopy, formalin-fixed skin sections from patients with bullous pemphigoid may be used to examine the presence of C3 deposition along the epidermal basement membrane zone, for the confirmation of the diagnosis. [63]

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      Histologic Findings

      The histopathologic examination demonstrates a subepidermal blister. The inflammatory infiltrate is typically polymorphous, with an eosinophil predominance. Mast cells and basophils may be prominent early in the disease course. Lesional skin biopsy specimens may reveal a predominantly neutrophilic infiltrate or minimal inflammation (pauci-inflammatory or cell-poor bullous pemphigoid).

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