Investigations
1st investigations to order
skin biopsy, haematoxylin and eosin stain
Test
Skin or mucosal specimens should include intact epidermis immediately adjacent to active blisters or erosions. Biopsies of erosions can often result in a false-negative test as there is no epidermis remaining for interpretation.
The skin biopsy is placed in a formalin-based solution for routine processing in a histopathology laboratory.
A biopsy demonstrating classic findings of pemphigus is generally diagnostic, but other conditions (e.g., benign familial pemphigus, Darier's disease, or transient acantholytic dermatitis) can demonstrate some of the histological hallmarks of pemphigus. However, these conditions are clinically distinct.
Result
histopathology findings suggestive of pemphigus: changes in epidermal, dermal, and basal cells; in pemphigus vulgaris (PV), the basal cells lose their adhesion to adjoining keratinocytes while maintaining adhesion to the basement membrane, giving a tombstone appearance; in pemphigus foliaceus (PF), superficial bullae with a split directly beneath the stratum corneum, often in the granular layer; in paraneoplastic pemphigus (PNP), histopathology findings suggestive of pemphigus (i.e., tombstone appearance of the basal cells), erythema multiforme, and lichen planus occur
skin biopsy, direct immunofluorescence
Test
This is the most pathognomonic test. Skin or mucosal specimens should include intact epidermis immediately adjacent to active blisters or erosions. If a biopsy is obtained from an erosion, no epidermis remains for interpretation and false-negatives can occur. False-negatives can also occur if the autoantibody titre is low. If pemphigus is strongly suspected and the skin biopsy is negative, the biopsy should be repeated or serum submitted for indirect immunofluorescence, serum ELISA, or immunoblotting.
The skin biopsy should be placed in a solution that does not contain formalin. The most commonly used transport mediums are Michel's and Zeus. The specimen is frozen, sectioned, and stained in a qualified immunodermatology laboratory.
PNP often demonstrates an immunofluorescence profile suggestive of pemphigus, bullous pemphigoid, lichen planus, or some combination of these. This mirrors the findings on routine haematoxylin and eosin staining. In rare cases of PNP, no immunoreactants are observed.
Result
Pemphigus vulgaris (PV) and paraneoplastic pemphigus (PNP): staining for IgG, C3, or both in a broad linear band on the surface of epidermal keratinocytes in the suprabasilar region of the epidermis (higher in the epidermis in pemphigus foliaceus[PF])
Investigations to consider
indirect immunofluorescence on serum
Test
Serum collection by venipuncture is preferred.
Indirect immunofluorescence (IIF) staining involves applying the patient's serum to a substrate. The presence of autoantibodies that characteristically stain the substrate strongly supports the diagnosis of pemphigus.
False-negative tests occur when the serum autoantibody concentration is below detection.
Some patients have evidence of autoantibodies but no evidence of active disease. Therefore, clinical correlation is required.
Result
immunofluorescence staining on the surface of keratinocytes on human skin substrate, monkey oesophagus, guinea pig oesophagus, or rodent bladder
serum ELISA
Test
Can be used to detect specific autoantibodies, particularly antibodies to desmoglein 1 and 3.
Serum collection by venipuncture is preferred. False-negative tests occur when the serum autoantibody concentration is below detection.
Serum ELISA can have considerable background, particularly in the presence of rheumatoid factor.
A positive test indicates disease. However, some patients have evidence of autoantibodies but no evidence of active disease. Therefore, clinical correlation is required.
Subsequent studies are rarely indicated.
Result
positive, based on the assay and the laboratory standard
upper gastrointestinal endoscopy
Test
Endoscopy is helpful in determining the extent of involvement or if the diagnosis is in doubt.
Findings of oesophagitis suggest a diagnosis of pemphigus. However, many patients with pemphigus do not have oesophageal involvement.
Result
erosive oesophagitis and biopsy supporting an acantholytic process; pemphigus vulgaris (PV), paraneoplastic pemphigus (PNP), lichenoid oesophagitis
CXR
Test
Patients with paraneoplastic pemphigus (PNP) often develop lung involvement.
Lung involvement is not observed in pemphigus vulgaris (PV) or pemphigus foliaceus (PF), but indicates PNP.
Result
findings suggestive of bronchiolitis obliterans
chest CT scan
Test
Patients with paraneoplastic pemphigus (PNP) often develop lung involvement.
Lung involvement is not observed in pemphigus vulgaris (PV) or pemphigus foliaceus (PF), but indicates PNP.
Result
findings suggestive of bronchiolitis obliterans
PFT
Test
Patients with PNP often develop lung involvement.
Lung involvement is not observed in pemphigus vulgaris (PV) or pemphigus foliaceus (PF), but indicates PNP.
Result
obstructive ventilatory defect in bronchiolitis obliterans (paraneoplastic pemphigus [PNP])
serum immunoblot (Western blot)
Test
Standard serum collection is preferred. False-negative tests occur when the serum autoantibody concentration is below detection. A subset of patients with PNP do not have detectable antibodies.
It has been proposed that some forms of PNP do not have associated autoantibodies and therefore are 'seronegative' forms of PNP.[33]
A positive test indicates disease. However, some patients have evidence of autoantibodies but no evidence of active disease. Therefore, clinical correlation is required.
Result
antibodies to components of the desmosome (pemphigus foliaceus [PF] and pemphigus vulgaris [PV]) and to hemidesmosome (paraneoplastic pemphigus [PNP])
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