Skin biopsy is arguably the most important single diagnostic technique in the diagnosis of skin disorders.

 Close cooperation between the clinical dermatologist and the diagnostic dermatopathologist is not only desirable but essential.

 In many conditions, the histological features are pathognomonic of a particular skin disorder. In others, the changes may be characteristic of, but not specific for, one specific disease.

Biopsy samples should be collected if...

1.  The therapy for the skin disorder is associated with significant side effects (to confirm the clinical diagnosis before starting therapy).

2.  A nodular lesion, ulcer, or nonhealing wound might represent a tumor (so that surgical excision of the tumor can be performed as early as possible).

3.  Lesions develop suddenly, are severe, or are unusual (to help identify a serious disease so that therapy can be instituted early).

4.  Lesions develop during the course of therapy (to identify a potential adverse reaction to drug therapy).

5.  There are multiple differential diagnoses, each with their own individual course of treatment.

6.  A skin disorder fails to respond to apparently appropriate therapy or the disorder responds to therapy but recurs when therapy is stopped.

Biopsy Sampling

1.  Preparation

a.  Very gently clip or scissor if necessary.

b.  Do not surgically prepare the site if sampling lesions in epidermis or dermis.

c.  Caveat: The site can be surgically prepared for excision of lesions deep in the subcutis or to remove a large nodular mass, such as a neoplasm.

2.  Lesions

a.  Collect multiple samples representative of the range of lesions.

b.  If crusting is significant, collect crust, wrap in lens paper, and place in formalin (e.g., pemphigus foliaceus).

c.  For alopecic conditions: Collect samples from the most alopecic areas and draw a line on the sample in the direction of the hair coat.

d.  For ulcers or depigmenting lesions (junction important): Use incisional or excisional method or use an 8-mm biopsy punch instrument, and draw a line on the sample perpendicular to the junction between lesion and normal skin.

3.  Punch samples

a.  Use 6- or 8-mm punch instruments for haired skin.

b.  Draw a line.

c.  Without the line, the sample could be cut at a right angle to the desired line and thus completely miss the lesional area.

d.  Use 4-mm punch for periocular skin, footpad, or nasal planum.

4.  Incisional and excisional samples

a.  Use incisional or excisional methods if a smaller punch would damage a larger pustule or vesicle.

b.  Gently place thin incisional or excisional samples, subcutis side down, on a piece of cardboard, let adhere for about 30 seconds, then place in formalin (prevents warping).

c.  Do not let the sample dehydrate.

d.  For lesions in the panniculus, use incisional or excisional methods to ensure that the sample is of sufficient size and depth for diagnosis.

5.  Fixation

a.  Fix samples in 10% neutral buffered formalin with 10 times the volume of formalin as the volume of the sample.

b.  For diagnosis of autoimmune skin disease or tumors, begin with standard histopathology. Selected immunohistochemical stains can usually be done later on formalin-fixed samples if desired.

6.  History

a.  Submit a history with differential diagnoses

i.  Age, breed, sex

ii.  Lesion distribution

iii.  Lesion appearance and severity

iv.  Lesion duration

v.  Treatment and duration of treatment

vi.  Influence of specific therapy and/or recent therapy that could alter lesions

vii.  Other clinical problems

viii.  Laboratory abnormalities

ix.  Clinical differential diagnosis (important)