Punch Biopsy
Punch biopsy removes a cylinder of skin, from the epidermis through the dermis into the superficial subcutaneous fat, using a hollow circular blade. Punches come in diameters of 1.5 to 8 mm, and 3 to 4 mm are used most often.
It is the main way of diagnosing inflammatory skin disease, blistering disease, vasculitis, connective tissue disease, infiltrative disease and infection, and it is suitable for small tumours. It samples the full thickness of the skin, so the pathologist sees the epidermis, dermis and fat together, in their normal relationships.
It is a quick bedside procedure under local anaesthesia and takes 5 to 15 minutes. It can be repeated at different sites, and a second sample can be taken for immunofluorescence or culture.
Histology gives a specific diagnosis in about half of inflammatory dermatoses, and a descriptive pattern with a differential in the rest, which is then combined with the clinical findings. Accuracy is highest for tumours, blistering disease and vasculitis.
Indications.
- Inflammatory dermatoses of uncertain cause (lichenoid, psoriasiform, spongiotic, granulomatous).
- Blistering disease: pemphigus, pemphigoid, dermatitis herpetiformis and epidermolysis bullosa acquisita.
- Cutaneous vasculitis and purpura.
- Connective tissue disease: lupus erythematosus, dermatomyositis and scleroderma.
- Panniculitis, if a deep enough sample can be taken.
- Alopecia (scarring and non-scarring), using a 4 mm punch with horizontal and vertical sections.
- Suspected infection (leprosy, leishmaniasis, deep fungal infection, mycobacterial infection), with tissue for culture.
- Cutaneous lymphoma and infiltrates.
- Small tumours not needing wide excision (basal cell carcinoma, squamous cell carcinoma, Merkel cell carcinoma), and lesions in a site where a larger biopsy is not practical.
- Genetic skin disease and amyloidosis.
Not indicated for a suspected melanoma when complete excision is possible, because a partial sample can miss the deepest part and leave an incomplete record of thickness.
Contraindications and precautions.
- Bleeding disorder or severe thrombocytopenia.
- Allergy to local anaesthetic.
- Infection at the site, which is avoided unless infection is the question.
- Sites needing care: over tendons, nerves and superficial vessels, the eyelid, the lip and the ear cartilage.
- Keloid tendency or poor wound healing, which affect the choice of site and size.
- Suspected panniculitis needs a deeper sample (a larger punch, or an incisional biopsy).
- Anticoagulants usually continue, with pressure afterwards.
Preparation and technique.
The most representative lesion is chosen. A well developed lesion that is untreated and not excoriated is best. For vasculitis, a lesion under 24 to 48 hours old is sampled, because older lesions lose the characteristic features.
For blistering disease, two samples are taken. One comes from the edge of a fresh blister (under 24 hours), including part of the intact skin, for routine histology. The second is perilesional skin, 1 cm from the blister, for direct immunofluorescence, placed in transport medium or sent fresh on saline.
The area is cleaned, local anaesthetic is infiltrated, and a punch of suitable size is pressed through the skin with a twisting motion until it gives way into the fat. The core is lifted gently with a needle or fine forceps, and cut at its base with scissors. Forceps pressure on the epidermis is avoided because it crushes the tissue.
Bleeding is controlled with pressure, an astringent, or a suture. Defects of 4 mm and more are usually sutured, and smaller ones are left to heal by secondary intention with a dressing. Sutures come out at 5 to 14 days, depending on the site.
