Tierdermatologie Deisenhofen Consultations
Seven tips to obtain a better skin biopsy result:

1. Do not prepare the skin surface (except nodule excision & deep tissue culture)
2. Spend 5 minutes looking for primary lesions to biopsy
3. Think about the differential diagnoses and write them on the submission form
4. Select multiple samples (4-6) that represent a
range from normal to worst
4. If possible, always include a normal sample from the lateral or dorsal trunk
5. Use 6 to 8mm punches or an excisional biopsy except on noses and feet
6. Handle the biopsy specimen carefully, treat it like tissue paper even when excising
7. Give the pathologist a complete history, physical findings as well as your differential diagnosis list

Please see below for some more detailed biopsy sampling guidelines

A skin biopsy is a "snapshot", a movie "freeze", a picture taken at one point in time:

It may help to remember that a skin biopsy is a selection of several areas of skin (which one hopes are representative of the range present) at a single point in time (the time of the biopsy sampling). It may be that this timepoint is not optimal with regard to the pathogenetic events. For example in pemphigus foliaceus, it may be that the actual acantholytic pustule formed and ruptured a week ago and there are now no diagnostic acantolytic pustules to be seen! The pathologist must then work with supportive clues, such as acantholytic cells in the crusts, rather than more specific changes.

Detailed biopsy sampling guidelines:

Which skin lesions should be biopsied?
Any skin lesion which appears unusual, especially if the onset is acute; lesions which fail to respond to empirical therapy; lesions that are nodular and those in which a diagnosis of neoplasia is suspected. Finally biopsies can be helpful to exclude diagnoses, even if one does not necessarily obtain a definitive diagnosis

Preparation of the site
With the exception of excisional biopsy of nodules, no surgical preparation of the site should be employed. Even topical application of alcohol with air drying may alter the epidermis. The overlying hair is clipped and gently removed. If crusts are present it may be less traumatic to use scissors than electric clippers,as they should be left on the skin, biopsied and a note 'please cut in crusts' should be added to the request form. Local anaesthesia can be administered subcutaneously with the needle entry point outside the biopsy area. Infection as a result of this lack of surgical preparation is rare.

Selection of the site
Spend 5 minutes looking for primary lesions and the full range of lesions. Carefully examine the entire animal for the most representative samples, and try to form a list of differential diagnoses prior to biopsy. Sample depigmenting lesions in an area of active depigmentation i.e. a grey color rather than the final stage of depigmentation which is white.
Sample alopecia in the centre of the worst area as well as in junctional and normal areas. Before the biopsy, draw a line on the skin in direction of the hair growth.
Sample areas of ulceration via an elliptical biopsy with the adjacent intact skin. The transition point between ulcer and intact skin may give clues for the cause IF it is to do with an epidermal disease such as a bullous dermatosis.
Always include a normal sample, if possible from the dorsal trunk, not ventrally.
Obtain multiple samples (6 is a good rule of thumb) so that they represent the range of lesions from normal to worst.

Handle the biopsy specimen carefully, treat it like "tissue paper" even when excising. The biopsy punch is held at right angles to the surface of the skin and gently placed over the selected lesion. Firm continuous pressure is applied and the punch is rotated in one direction (!) until a sufficient depth has been reached to free the dermis from its underlying attachment. The punch is removed and any blood carefully blotted. The section of tissue is grasped gently at the base - which should be the panniculus - and subcutaneous attachments severed. Under no circumstances should the dermis or epidermis be grasped with forceps as this leads to 'crush artifact', destroying the cells and architecture of the sample.
In the case of a thin sample, it should then be placed - panniculus down - onto a rigid piece of cardboard or piece of tongue depressor. This prevents the tissue from curling when placed in the formalin. Wait two minutes for the tissue to dry onto the cardboard a little and then place it tissue side down, cardboard side up in the formalin. The volume of formalin required is approximately 10 times the volume of the sample. Large nodules can be partially transected @ 1cm intervals to allow adequate penetration of the formalin into the centre of the lesion - but most important!! -leave the base of the nodule attached, do not cut completely through the nodule, so that the architecture is retained.