Direct Immunofluorescence Patterns in Skin Disease
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Direct answer
Direct immunofluorescence on skin detects immunoglobulin and complement deposited in the tissue of a patient, and the location of the deposit defines the disease. Intercellular deposits in a fishnet pattern point to pemphigus, while linear deposits along the basement membrane zone point to bullous pemphigoid. Granular IgA in the dermal papillae is the classic finding in dermatitis herpetiformis.
What you must remember
- Fishnet or chicken-wire pattern: intercellular IgG and C3 in the epidermis, typical of pemphigus vulgaris and pemphigus foliaceus.
- Linear basement membrane pattern: IgG and C3 along the basement membrane zone, typical of bullous pemphigoid, mucous membrane pemphigoid and pemphigoid gestationis.
- Linear IgA pattern: IgA along the basement membrane zone, seen in linear IgA bullous dermatosis.
- Granular papillary dermal pattern: IgA in the dermal papillae, the hallmark of dermatitis herpetiformis, which is linked to gluten sensitivity.
- Lupus band: granular IgG and IgM with C3 at the dermoepidermal junction, best seen in sun-exposed non-lesional skin of lupus erythematosus.
- Salt-split skin: IgG on the epidermal roof suggests bullous pemphigoid, while IgG on the dermal base suggests epidermolysis bullosa acquisita.
- Sampling: take a fresh perilesional sample and transport it in Michel's medium, because necrotic lesions give nonspecific results.
Matching deposit to disease on the report
The pattern of deposition matters more than the presence of an immunoglobulin, because most of these diseases show IgG or C3 somewhere. Read the immunoreactant and its location together, then check the report against the clinical picture.
| Pattern | Main immunoreactant | Typical disease |
|---|---|---|
| Fishnet, intercellular | IgG and C3 | pemphigus vulgaris |
| Linear basement membrane | IgG and C3 | bullous pemphigoid |
| Linear basement membrane | IgA | linear IgA bullous dermatosis |
| Granular papillary dermal | IgA | dermatitis herpetiformis |
| Granular at dermoepidermal junction | IgG, IgM and C3 | lupus erythematosus |
Salt-split skin separates the basement membrane zone, so the side that carries the IgG tells you the level of the blister. A roof-side pattern points to bullous pemphigoid, while a base-side pattern points to epidermolysis bullosa acquisita. Immunofluorescence is a confirmatory test, so it is read alongside histology and serum antibody results.
Specimen handling is a frequent exam point, because fresh tissue preserves the deposits while dried or necrotic tissue does not. A negative result is informative only when the site and timing of sampling were appropriate.
Where the immunofluorescence trap catches candidates
Patterns look alike on a report, and examiners use that similarity to set traps.
- Trap: reading intercellular IgG as bullous pemphigoid Correct: intercellular deposits form the fishnet pattern of pemphigus, whereas bullous pemphigoid shows linear deposits along the basement membrane.
- Trap: assuming granular IgA means IgA pemphigus Correct: granular papillary IgA is dermatitis herpetiformis, whereas IgA pemphigus shows intercellular IgA.
- Trap: sampling the necrotic centre of a blister Correct: take a fresh perilesional sample, since necrotic tissue gives nonspecific staining.
- Trap: treating a negative DIF as excluding the disease Correct: a false negative is possible if the sample is taken late, from a healed site or from the wrong area.
Frequently asked questions
Which DIF pattern is seen in dermatitis herpetiformis?
Dermatitis herpetiformis shows granular IgA deposits in the dermal papillae on direct immunofluorescence of perilesional or uninvolved skin. This finding is the diagnostic hallmark of the condition, which is linked to gluten sensitivity.
How does salt-split skin help separate bullous pemphigoid from epidermolysis bullosa acquisita?
Salt-split skin separates the basement membrane zone, so IgG deposits can be located on either the epidermal roof or the dermal base. Roof-side IgG indicates bullous pemphigoid, while base-side IgG indicates epidermolysis bullosa acquisita.
Where should a skin sample for direct immunofluorescence be taken?
A sample for direct immunofluorescence should be taken from fresh perilesional skin, avoiding the necrotic centre of a blister. It should be transported in Michel's medium, as the immune deposits can be lost if the tissue is dried or damaged.
What is a lupus band on direct immunofluorescence?
A lupus band is a granular deposit of IgG, IgM and C3 along the dermoepidermal junction. It is best seen in sun-exposed non-lesional skin of patients with lupus erythematosus, and it supports the diagnosis when read with the clinical picture.
Which DIF pattern distinguishes pemphigus vulgaris from bullous pemphigoid?
Pemphigus vulgaris shows a fishnet pattern of intercellular IgG and C3 throughout the epidermis, whereas bullous pemphigoid shows linear IgG and C3 along the basement membrane zone. This difference reflects whether the target antigen lies between keratinocytes or at the basal hemidesmosomes.