Nail matrix biopsy
What is nail matrix biopsy?
Nail matrix biopsy is a surgical procedure in which a tissue specimen is obtained from the growth plate of a fingernail or toenail.
Why is nail matrix biopsy undertaken?
Nail matrix biopsy is undertaken to make or confirm a diagnosis or to surgically remove a skin lesion that is affecting the growth nail plate. The following list describes some conditions in which this procedure may be undertaken.
- To distinguish inflammatory conditions like nail psoriasis and lichen planus
- To identify benign tumours like myxoid cyst, viral wart and onychomatricoma
- To find out the cause of a solitary melanonychia, a pigment band on the nail plate, which may be due to a benign pigmented lesion or melanoma of the nail unit
- To make a diagnosis of squamous cell carcinoma or squamous cell carcinoma in situ
- To diagnose other nail disorders.
How is a nail biopsy done?
Nail biopsy is usually undertaken under local anaesthetic. This is injected locally or more often by digital block, when the anaesthetic is injected through the webspaces along each side of the finger or toe.
Various techniques are used to biopsy the nail matrix. The nail plate may be removed for examination, or replaced after the procedure. Here we provide a step by step guide to the “trap door” or “pop the bonnet” technique for biopsy of pigmented nail matrix lesions. This allows a direct view of the nail matrix permitting precise targeted biopsy of the lesion.
- After local anaesthetic has been injected as a digital block using lignocaine without adrenaline, a tourniquet is applied to reduce bleeding. The time the tourniquet is applied is recorded. The proximal nail fold is completely cut through on each side approximately halfway back to the distal interphalangeal joint (figure 1).
- The nail plate is separated from the nail bed with a Freer elevator, taking care to keep distal to the lunula (the half-moon) to avoid injuring the nail matrix (figure 2).
- The nail plate is hinged up vertically like a car bonnet being opened (figure 3).
- The nail bed has been injured by the procedure but the nail matrix is clearly and completely seen in pristine condition. Parallel lines of pigmentation can be seen in this case. The biopsy can be targeted to include a complete longitudinal sample of this portion of the nail matrix (figure 4).
- The nail plate is retracted with a suture anchored on the tourniquet. The biopsy specimen is scored with a scalpel then shaved at least 1-mm thick. This is adequate for dermatopathological assessment if the lesion is thought to be thin. Extreme care is taken to avoid crushing the sample with forceps (figure 5).
- The biopsy specimen is placed in formalin in a specimen container. The request form should carefully describe the lesion and the procedure. The specimen must be accurately labelled. It is recommended that the pathologist is directly contacted to ensure correct processing of the specimen (figure 6).
- A suture is placed in each of the incisions (figure 7).
- A suture is placed to hold the nail plate onto the nail bed (figure 8).
- The tourniquet is removed and the tourniquet removal time should be recorded.
- After removing the sutures a week later, the nail plate is vulnerable to “popping” and can be supported with tape.
What are the risks of nail biopsy?
Nail biopsy can lead to any of the usual complications from a surgical procedure, such as bleeding, infection, scarring, incorrect diagnosis and incomplete removal of a tumour.
Scarring of the nail matrix is common and may result in permanent deformity of the nail plate. This is inevitable if the width of a full-thickness nail matrix biopsy is greater than 3 mm.