Laboratory Studies
Routine serologic studies are not helpful in diagnosing pemphigoid gestationis, although peripheral eosinophilia may be seen in some cases.Laboratory values that may be non-specifically elevated include immunoglobulin levels, erythrocyte sedimentation rates, acute-phase reactant levels, and antithyroid antibodies. [17]
Immunoblotting and enzyme-linked immunosorbent assay (ELISA) testing are sensitive tools for the detection of autoantibodies to BP180 antigen in patients with pemphigoid gestationis. ELISA may have utility for monitoring autoantibody serum levels, which correlate to disease activity. [18]
Notably, HLA-DR3/DR4 is present in 45% of patients with pemphigoid gestationis, as compared with 3% of the general population. [8]
Histologic Findings
Histologic features vary with the clinical lesion present. In urticarial plaques, there is a predominantly perivascular infiltrate composed of lymphocytes, histiocytes, and eosinophils with marked papillary dermal edema (which may result in a “teardrop” appearance), with occasional spongiosis and basal keratinocyte necrosis. Vesicles and bullae of pemphigoid gestationis classically exhibit subepidermal blister formation with an eosinophilic infiltrate. The affected dermis contains a perivascular infiltrate composed of eosinophils, lymphocytes, histiocytes, and rare neutrophils.
Direct immunofluorescence (DIF) should be performed using samples from uninvolved perilesional skin and will show linear C3 along the basement membrane zone (essentially universally present) with linear IgG in 30-50% of patients. DIF is key to differentiate pemphigoid gestationis from polymorphic eruption of pregnancy, also known as pruritic urticarial papules and plaques of pregnancy (PUPPP).
Using the salt-split skin technique, indirect immunofluorescence (IIF) can be used to detect linear immunoglobulin G deposition along the epidermal side (roof), which is seen in approximately 30% of patients. Complement-added indirect immunofluorescence will detect circulating anti-basement membrane immunoglobulin G1 antibodies in the serum for virtually all patients with pemphigoid gestationis. [2, 19, 20]
Recently, immunohistochemical staining for C4d at the dermoepidermal junction on routine H&E tissue has been demonstrated to be sensitive and specific for PG, allowing a single skin biopsy to serve the purposes of both histopathological examination and immunohistochemistry. [21]
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Tense bullae are present on the arms of this otherwise healthy 32-year-old primigravida woman.
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Urticarial or hivelike plaques, as seen on the posterolateral neck of this woman in her third trimester, can be observed in patients with pemphigoid gestationis.
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Upon histologic evaluation, an incipient blister is present at the junction of the epidermis and dermis, as is a moderately dense perivascular inflammatory infiltrate.
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A close-up view of a blister reveals the tense primary lesion filled with clear fluid.
