A skin biopsy is one of the most important tools in the diagnosis and management of skin diseases. It involves removing a small piece of skin for evaluation under the microscope by the pathologist.
A skin biopsy is a simple procedure that provides valuable information to help confirm disorders including skin cancers, various skin lesions or rashes. It can help to form an appropriate treatment plan – one that is tailored to the exact skin condition.
This is usually performed in the medical practitioner’s office under local anaesthesia. The skin at the biopsy site is marked and cleaned. The local anaesthesic injection produces a transient stinging sensation. After the skin specimen is collected, the clinician may close the wound with a suture if needed and a dressing may be applied.
Blood thinning medications like Warfarin do not need to be stopped for skin biopsies. An international normalized ratio (INR) between 2.5 – 3.0 is generally accepted for a simple skin biopsy. Similarly stopping of aspirin or clopidogrel is not necessary, but you must inform your doctor so that they can ensure that equipment for controlling the bleeding is available.
The chosen biopsy site is usually marked with a surgical marker pen to ensure that the site is still visible after local anaesthesic injection. The area is then cleaned with a disinfectant. These can include alcohol, povidone-iodine solution and chlorhexidine.
The local anaesthesic is usually injected using a 28 or 30-gauge needle, which is one of the smallest needles available. This can cause a stinging sensation, which is short. Usually 1-2% Ligoncaine with adrenalin is used. Other options are mepivacaine and bupivacaine depending on patient allergies.
Topical agents such as EMLA cream (a mixture of prilocaine and licodaine) or 4% lidocaine cream can be used in combination with injected local anaesthesia to help with pain relief.
There are 4 types of biopsies commonly used. These are shave, punch, incisional and excisional biopsy. Choosing the best form of biopsy technique requires knowledge of the level of lesion in the skin such as epidermis, dermis or subcutaneous tissue. Figure one illustrates the levels of skin reached by the common techniques.
Shave biopsies are quick to perform and do not require suturing for closure. It is most suited for lesions elevated above the skin surface. This technique can rarely leave a depressed scar. The skin is left to heal by itself without a suture.
This is ideal for diagnostic purposes as it produces full thickness skin specimens. It is easy to perform and gives a uniformly shaped tissue. This type of biopsy is performed using an instrument called a “punch” which is a circular blade attached to a pencil like handle. The blade size ranges from 2mm – 8mm in diameter. A punch of 3-4 mm is sufficient for most conditions. Small diameter biopsies such as 2mm are sometimes used for cosmetically sensitive sites such as the face. A suture may be used to help in wound healing. Generally the wound is closed with suturing. Sutures on the face can be removed in 5 to 7 days whereas the ones on the other areas in 1 to 2 weeks.
Incisional and Excisional biopsy
These types of biopsies are used when a sizable quantity of tissue is needed to obtain the best information about a skin condition. An incisional biopsy means only part of the skin condition is removed where as an excisional biopsy means the whole skin lesion is removed. This is highly useful in diagnosing conditions such as melanoma as well as deeper skin lesions. Skin sutures are used to close the wound together.
A reaction to the local anaesthetic: Having a reaction to the local anaesthetic agent is very rare. However, sometimes a reaction to an additive within the local anaesthetic may occur.
Bleeding: This may sometimes occur especially on the scalp and face. It is more common in patients on blood thinner medications (aspirin, clopidogrel, warfarin) and with over the counter use of fish oil, garlic, gin-seng supplementation. In a skin biopsy the bleeding tends to stop quickly with the application of pressure for 2-3 minutes.
Damage to other structures: Damage to nerves and vessels is rare. A biopsy in the pre-auricular areas can occasionally damage the facial nerve branches which are superficial.
Infection: With appropriate after care such as salt-water washes, this is not common. A wound infection is usually caused by the bacterium Staphylococcus aureus. There is an increased risk of infection in areas like the groins, axillae and legs as well as with immunosuppression and diabetes.
Scarring: A skin biopsy may leave a small scar. There is a small risk of keloid scarring over the shoulders and chest region.
Delayed healing: This occurs when the wound takes longer than expected to heal. Slow healing may occur in diabetic patients or with an infection, especially on the lower extremities.
The skin specimen is placed in a jar containing the fixative formalin and sent to a pathology lab. It generally takes between 1-2 weeks for the report to be ready. Unfortunately, in some cases the report may be inconclusive, meaning that an exact diagnosis cannot be made. However, sometimes there is enough information in the biopsy result which, combined with the clinical findings, can help with a diagnosis. In certain conditions, repeat biopsies may be required.
There are a number of additional tests that can be performed by the pathologist, including direct immunofluorescence (DIF) and microbiological culture.
This information has been written by Dr Linda Chan and Dr Elizabeth Dawes-Higgs