Differentiation of bullous pemphigoid (BP) from epidermolysis bullosa acquisita (EBA) and other forms of BMZ autoimmunity

By E.H. Beutner, PhD and Richard W. Plunkett, PhD
Beutner Laboratories
Buffalo, New York

Diagnostic tests

If clinical findings point to a need to differentiate BP or other forms of pemphigoid from EBA or other forms of basement membrane zone (BMZ) autoimmunity, select tests based on direct and indirect IF findings. These include: 1) "salt split biopsy" tests, 2) type IV collagen and laminin test and 3) indirect IF serum test normal "salt split skin."

Clinically, BP, EBA and related autoimmune diseases of the BMZ can take multiple forms. These include urticarial, cicatricial and gestational pemphigoid as well as lichen planus pemphigoides and linear IgA bullous dermatosis and related disorders with hemidesmosome autoantibodies; these need to be differentiated from EBA, bullous LE and related autoimmune diseases of deeper BMZ components which may be more difficult to manage.

  • Primary diagnosis In this diverse group of disease, diagnosis depends on a combination of clinical findings, typically of bullous, vesicular or urticarial lesions and direct IF and serum studies that reveal antibodies to the BMZ. (See UPDATE).*

  • Differentiation If clinical findings point to the need to rule out EBA, bullous LE or other disorders such as the epiligrin form of cicatricial pemphigoid, follow-up laboratory studies are indicated. Selection of methods depends on the presence or absence of lesions in the specimen examined by direct IF and the detection of BMZ antibodies in serum tests.

Selection of methods for differentiation of pemphigoid from EBA

1. The "salt split biopsy" method entails placement of biopsy specimens in 1M NaCl for 24 hours and splitting them at the lamina lucida by traction. This method can be used if the specimen taken for direct IF studies has IgG and/or IgA deposits in the BMZ of normal skin or mucosa.

  • The detection of IgG (and/or IgA) deposits in the BMZ of the epidermal roof or roof and floor of the split is diagnostic of pemphigoid or linear IgA bullous dermatosis (LABD) if predominantly IgA appears in the BMZ. Such salt split biopsy patterns characterize hemidesmosome "BP" antigens.

  • The detection of IgG (and/or IgA) deposits exclusively in the BMZ of the dermal floor of the split is diagnostic of EBA, bullous LE (or possibly of the epiligrin form of autoimmunity in cicatricial cases). Such a salt split biopsy reaction pattern characterizes the sub-lamina densa antigen of EBA, notably type VII collagen, in anchoring filaments.

Limitations of salt split biopsy method: Specimens with multiple, subepidermal (or sub-epithelial) vesicles or parts of bullae cannot be used for this "salt split biopsy" method because the split induced by traction cannot be distinguished from the pre-existing vesicles or bulla. The distribution of IgG and/or IgA in the BMZ of the roof or floor of bullae or vesicles has no differential value in distinguishing pemphigoid from EBA.

C3 deposits in the BMZ give a less clearly interpretable distribution following splitting than deposits of IgG or IgA; they tend be more evenly distributed in the BMZ of the epidermal roof and dermal floor.

* See UPDATE on "Pemphigoid and related autoimmune diseases: Diagnosis with biopsy and serum studies". (This UPDATE also lists references).

2. The type IV collagen and laminin methods entail the use of indirect IF tests for these BMZ markers on sections of biopsy specimens that include small, fresh subepidermal (or subepithelial) vesicles. These BMZ markers can be used only on biopsies with vesicles or clefts due to a Nikolsky sign (and have BMZ deposits of IgG, IgA and/or C3).

In such specimens, type IV collagen and laminin can be detected in the BMZ above the lamina densa in fresh, naturally occurring vesicles or clefts.

  • The localization of type IV collagen and laminin in the BMZ of the dermal floor of vesicles is a sign that the lesion developed above the lamina densa. This is consistent with pemphigoid or the common form of LABD.

  • The localization of type IV collagen and laminin in the BMZ of the epidermal roof of fresh vesicles is a sign that the split developed below the lamina densa. This is characteristic of EBA, the EBA form of LABD, bullous LE or, in cicatricial pemphigoid, of epiligrin autoimmunity. Limitations of BMZ marker studies. These methods can give misleading results if used on biopsy specimens with fully developed bullae because EBA and bullous LE bullae can give false BP like reactions in such specimens. This may be due to secondary effects of lytic enzymes from inflammatory cells which can induce the formation of clefts in the lamina lucida in such lesions. Thus, this method should be used only for specimens with small, fresh vesicles or clefts.

3. Indirect IF tests on "salt split skin" entail serum studies on normal skin treated with 1M NaCl for 24 hours and then split by traction and cut. Such studies can be used if biopsy specimens include fully developed bullae which preclude the use of the above listed "salt split biopsy" or BMZ marker studies. They can also serve to confirm findings by the "salt split biopsy" and/or with the BMZ marker methods.

  • The finding of a reaction of antibodies of the IgG or IgA isotype in the BMZ of the epidermal roof alone or together with a similar reaction in the BMZ of the dermal floor of the split is consistent with BP or a related form of pemphigoid (or LABD) with hemidesmosome autoimmunity.

  • The finding of a reaction of antibodies of the IgG or IgA isotype in the BMZ of the dermal floor of the split is consistent with EBA or bullous LE or, in cases of cicatricial pemphigoid, with epiligrin autoimmunity.

In cases of bullous LE, serum studies can also reveal the characteristic complement fixing ANA which help to rule out biologic false positive ANA that. occur commonly in BP and EBA and aid in characterizing bullous LE.

Limitations of indirect IF tests on "salt split skin": While this method is more cost effective than the two, above listed, biopsy study methods, positive serum reactions can be detected with only about 70% of BP sera and in smaller percentages of the other autoimmune diseases of the BMZ.

If there is need to rule out EBA or bullous LE in sero-negative cases in which direct IF biopsy specimens include fully developed bullae, repeat direct IF studies of a perilesional normal biopsy specimen are indicated.

Limitations of all three methods of differentiating BP and related forms of hemidesmosome autoimmunity from EBA, bullous LE and other forms of sublamina densa autoimmunity: While combined serum and biopsy studies with the use of the above three methods clearly differentiate the major forms of BMZ autoimmunity in over 90% of cases, some cases pose problems:

  • Linear BMZ deposits of IgM poses an unresolved diagnostic problem. Such cases may be referred to as linear IgM bullous dermatosis, but this is not a characterized clinical entity. IgM deposits may localize in the BMZ of the dermal floor in salt split biopsy tests in EBA, but they disappear in salt split testing of most biopsy specimens. While other explanations have been considered, none is proven.

  • BMZ deposits in bullous LE may be of the BP type or they may be absent, although they are typically of the EBA type. Cases with clinical signs of bullous LE and no detectable BMZ deposits may have Rowell syndrome.

  • In rare cases, BMZ autoimmunity may be due to other antibodies.**
    ** For added references, see UPDATE on Bullous pemphigoid versus epidermolysis bullosa acquisita and bullous LE.

Copyright © 1999 Beutner Labs, Inc.
 Published with permission.