Information on the skin biopsy
The timing of the biopsy
Direct immune fluorescence
If a biopsy is to be performed for the direct
immune fluorescence purposes, peri-lesional skin is more suitable
than the lesion itself in the case of blister-forming dermatoses.
As the tissue for the immune fluorescence is not fixed in
formalin and embedded in paraffin, but is instead frozen and
cut using the cryostat, striking 
artifacts
will appear. In a biopsy of blisters, this frequently leads
to total loss of the top of the blister, making a confident
assessment more difficult. Moreover, inflammation cells can
cause false negative results through phagocytosis of immune
complexes.This has been observed in particular in Dermatitis
herpetiformis cases, and led to the recommendation that biopsies
for immune fluorescence should be taken some distance from
active lesions. On the other hand, biopsies when there is
suspected bullous pemphigoid or pemphigus disease may be performed
peri-lesionally directly.(16) This may be done either by a
spindle biopsy which includes both a small blister for the
normal histology and peri-lesional skin for the immune fluorescence,
divided up and fixed appropriately following excision, or
by two closely-adjacent punches which are subsequently tied
together by a small incision, which results in a biopsy wound
that can readily be closed up by displacing the edges of wound
obliquely.(10)
When there is suspected chronic disciform
Lupus erythematosus, the tissue for the immune fluorescence
should as a matter of principle be sourced from the affected
skin. Since in the case of Lupus erythematosus residues of
immune globulins and a complement at the dermo-epidermal junction
can appear in clinically unaltered skin and thus point to
a systemic involvement, a biopsy of clinically unaltered skin
may be also performed where this suspicion exists (preferably
from light-exposed shoulder skin or back of the lower arm).
A
normal histopathological examination at the direct immune
fluorescence is always required, which is generally
much more meaningful and allows a proper assessment if a portion
of the tissue or a separate biopsy is fixed in formalin. A
normal histological post-examination of the material removed
and fixed for the immune fluorescence on its own is not adequate
for a precise histopathological diagnosis!
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