Punch skin biopsy for children with neuromuscular disorders

A punch skin biopsy is a short procedure to remove a small piece of skin tissue. This page from Great Ormond Street Hospital (GOSH) explains what a punch skin biopsy involves for children with neuromuscular disorders and what to expect when your child has one.

The sample of skin taken during the biopsy can be examined under a microscope or used to grow cells from the underneath surface (fibroblasts) of the skin. These cells can be tested for abnormalities of the DNA or to show whether a specific chemical reaction can or cannot take place.

A punch skin biopsy is usually carried out to determine or confirm a diagnosis. There are also certain metabolic or chromosome disorders that can only be diagnosed by a skin biopsy. The doctors will discuss the reason for your child’s biopsy with you.

Your child will usually have a skin biopsy as a day case on the ward. This means your child will arrive at the hospital, have the procedure and go home on the same day unless further investigations or treatment is needed. If your child is having another procedure under a general anaesthetic or sedation, the biopsy can be done at the same time.

The nurse caring for your child will see you when you arrive on the ward to explain the procedure in more detail, discuss any questions or concerns you may have and ask you to give your permission for the procedure by signing a consent form. If your child has any medical problems, for instance, allergies, please tell the nurse about these.

The person bringing your child to the test should have ‘Parental Responsibility’ for them. Parental Responsibility refers to the individual who has legal rights, responsibilities, duties, power and authority to make decisions for a child. If the person bringing your child does not have Parental Responsibility, we may have to cancel the test.

Skin biopsies are usually done while your child is fully awake, although the area of skin where the biopsy is taken will be numbed. Some children are worried by the procedure but you can help to distract your child by reading a story, playing a game or singing a song.

Depending on the area being biopsied, younger children can sit on your lap during the procedure. The biopsy takes about a minute. The biopsy site is numbed using a cream or spray before a local anaesthetic is injected. Once the area is completely numb, the nurse or doctor will clean it with an antiseptic wipe.

The punch skin biopsy needle is gently inserted into your child’s skin, rotated and a small circle of skin is carefully removed. The sample of skin will be sent to the laboratories for examination under a microscope and/or to grow cells from the underneath surface.

The biopsy site usually bleeds slightly straight after the procedure, but this will stop when pressure is applied to the site. The area will be held closed by Steri-Strips®, which are like strong sticky plasters, and then covered with a dressing.

There is a very small chance that the biopsy site may become infected afterwards. A child with known immune problems may be given an antibiotic cream to put on the area after the dressings and Steristrips® have been removed.

There is a chance that a scar, similar to a chicken pox scar, may form. This is more likely if your child has scarred easily in the past.

After the biopsy, you and your child will be able to go home unless any further treatment is needed.

The biopsy site may feel uncomfortable for a day or two afterwards. Your child may need paracetamol given according to the instructions on the bottle, unless you have been advised otherwise.

After five days, you can remove the dressing. The Steri-Strips® may fall off of their own accord – otherwise they can be soaked off in the bath or shower when you remove the dressing. Your child can go back to nursery or school the day after the biopsy, but the area could be a bit sore if it is knocked.

You should call your family doctor (GP) or the ward:

• • If the biopsy site is still painful more than three day after the biopsy was taken and normal pain relief does not work
• • If the biopsy site is red or angry-looking 
• • If your child develops a high temperature and is not eating

Growing fibroblasts often takes four to six weeks, so results of biochemical testing may be available within six to eight weeks. However, some of the more specialised biochemical tests have to be sent away to a specialised laboratory, which only do tests infrequently, so can take up to six months to come back.

Analysis of the genes responsible for a disease (carried on the DNA) can also take several months. We will tell you when you can expect to have the results.