Cutaneous disorders are among the most common conditions presented to primary care doctors. Many are easily identifiable and may be dealt with effectively without the need for cutaneous biopsy. Nevertheless, in many instances the diagnosis is not obvious on clinical grounds. The rash may display atypical features or may not respond to therapy as predicted.
In these cases, and when dealing with cutaneous tumours or worrying pigmented lesions, cutaneous biopsy with histological assessment becomes necessary.
The art of cutaneous biopsy is to derive the maximum amount of information from the minimum amount of tissue, causing least discomfort to the patient. This will be achieved if due regard is given to the advantages and shortcomings of the various techniques available for biopsying cutaneous tissue, and if the pathologist is supplied with a good clinical history.
For several reasons, clinical history assists greatly in the interpretation of skin biopsies. Clinicopathological correlation is particularly important in many inflammatory cutaneous disorders. As the histological features can be very similar, clinical notes may help us to arrange a list of provisional diagnoses in order of likelihood.
The key features to discuss with regard to cutaneous rashes include:
As there is wide variation in the normal microscopic picture from different sites, the area biopsied should also be stated.
For biopsies performed to distinguish between squamous cell carcinoma and keratoacanthoma, the rate of growth of the lesion is important.
When sending specimens of pigmented lesions, the degree of clinical suspicion should be stated, together with any history of melanoma within the individual or within the individual’s family. Any condition associated with cutaneous disorders, such as systemic lupus erythematosus, pregnancy or bone marrow transplant, should be mentioned in the clinical notes. The clinical history should also include the type of biopsy procedure used (see below) as this determines the way we handle the specimen in the laboratory. For example, the whole of an incisional biopsy will be blocked in order to gain the maximum amount of information, whereas an excisional biopsy will be transversely sectioned in order to fully assess the lateral excision margins in the case of a tumour biopsy.
This is the best technique to use for pigmented lesions and cutaneous tumours.
It allows for histological assessment and diagnosis of the lesion, and assessment of surgical excision margins. If appropriate, an orientation suture can be placed at one end of the excision, e.g. the superior end of the specimen, so that if the excision is inadequate, the margin involved can be indicated on an accompanying diagram.
Occasionally, excision biopsy is appropriate for inflammatory cutaneous disorders where the condition is characterised by the formation of vesicles. The best chance of removing an intact vesicle (which greatly aids diagnosis) may be through excision.
With incision biopsy, a thin elliptical biopsy is taken radially through the edge of the tumour or through the edge of a macular or annular rash.
Incision biopsy is superior to punch biopsy for diagnosing rashes, more tissue is displayed on histological section and scarring is often reduced. A typical incision biopsy is 5-6 mm in length and about 2 mm in width. It should be deep enough to extend into the subcutaneous adipose tissue. The biopsy should run radially from the centre or central areas of the lesion to include approximately 1 mm of normal cutaneous tissue surrounding the lesion.
Punch biopsies are easier to perform and, in general, are more convenient. Nevertheless, they nearly always yield less information than an incision biopsy.
For tumours, the biopsy should be taken centrally.
For cutaneous eruptions, the biopsy should be taken from an area typical of the rash. In some cases, multiple biopsies may increase the amount of information. In this procedure, it is best not to include normal skin.
Punch biopsies come in various sizes. As 2 mm punches often yield inadequate information for diagnosis, a 3 mm punch biopsy is the smallest that should be used.
This technique is suitable for superficially-located lesions with plaque-like clinical features, e.g. seborrhoeic keratoses.
It is not an appropriate technique for nodular lesions, cutaneous rashes or melanocytic lesions.
Preparation of the skin surface:
Be gentle when cleaning the skin surface prior to biopsy; try not to disturb any overlying scale as the keratin layers sometimes contain diagnostic information (e.g. this is where dermatophytic fungi may be seen).
Let any alcohol preparation dry before collecting specimens for immunofluorescence.
Only a small amount of local anaesthetic is required for punch biopsy procedures (0.5 mL maximum). Too much local anaesthetic within the tissues can distort the histological appearances and simulate dermal oedema.
Marking the lesion:
It is often prudent to mark the target area for biopsy with an ink marker, as some lesions can blanch following introduction of local anaesthetic. The erythema in many lesions is due to vascular dilatation occurring as part of the inflammatory disorder. Local anaesthetic can cause vasoconstriction and diminish the erythema clinically. This may result in a poorly targeted biopsy yielding subdiagnostic histology.
Depth of biopsy:
It is best to continue into the subcutaneous adipose tissue so that the entire dermis is represented on histological section. This helps greatly with the categorisation of many inflammatory skin disorders and also demonstrates the deep border of any cutaneous tumour. When performing a punch biopsy, the biopsy instrument appears to ‘give’ when it penetrates the dermal connective tissue into subcutaneous adipose tissue. A similar sensation will be noticed when dissecting free an incision biopsy.
Care with biopsy tissue:
All too often, after biopsy tissue has been retrieved from the patient, crush artefact occurs during its transfer into formalin. Crush artefact greatly distorts the histological appearance and repeat biopsy may become necessary.
Rather than grasping the biopsy tissue with non-tooth forceps, it should be transferred to the specimen container using needle tips, a skin hook or fine forceps, delicately grasping one edge of the biopsy.
Ordinary blue, 10% buffered formalin supplied with the specimen jars is suitable for nearly all cutaneous biopsies, except those submitted for microbiological culture or immunofluorescent examination.
Please label all specimen containers with the patient’s name and details, which should match those stated on the request slip. Unlabelled specimens can still be processed and interpreted if they arrive with labelled paperwork; however, the medico-legal status of any generated report is doubtful. The report will usually be generated with a ‘specimen received unlabelled’ comment attached.
Diagnosing cutaneous conditions can be challenging. The chances of success are improved when the clinician, is armed with a variety of biopsy techniques for use in the correct clinical setting, and when the pathologist is supplied with an adequate clinical history.
– General Practice Pathology is a regular column each authored by an Australian expert pathologist on a topic of particular relevance and interest to practising GPs. The authors provide this editorial free of charge as part of an educational initiative developed and coordinated by Sonic Pathology.