The skin punch
biopsy is a useful tool in the diagnosis of skin problems when used as part
of a thorough workup. It can be used to aid in the diagnose of autoimmune
diseases, hair loss diseases, infections, and sometimes allergies, as well
as other conditions. Sometimes the biopsy is nondiagnostic too.
1. How much discomfort does a skin biopsy cause and will there be a scar?
Other than the discomfort your dog feels when given the local anesthetic,
a skin biopsy is a painless procedure. Most biopsies, including the 6 mm diameter
biopsies needed for SA screening, are taken using a local anesthetic very
similar to that used in your dentist’s office. For each biopsy needed, a
small amount (at most a quarter of a teaspoon) of anesthetic will be injected
under the skin at the site to be sampled.
As you probably know from the dentist, the anesthetic can sting while being
injected, but soon afterwards the site is numb for hours. The needle used
to inject the anesthetic is small and causes only a small pinprick when inserted
into the skin. Once the skin is numbed, your dog should not feel any discomfort
for the rest of the procedure. To take the biopsy, a simple instrument called
a biopsy “punch” is used. The “punch” consists of a hollow, cylindrical blade
attached to a plastic handle. The blade is placed on the skin and with pressure
and a circular wrist motion, it is used like a cookie cutter to remove a core
of skin. The biopsied site will bleed a small amount but this usually stops
after a few minutes.
After the cylindrical plug of skin has been removed, one or two skin sutures
will be placed to close the biopsy site. Again, because of the local anesthetic,
your dog will not feel the suturing. Once the biopsy site is closed, it should
not be painful to your dog. After seven to 10 days the site should be healed
and the sutures will need to be removed — a process that only takes a few
seconds. Because the biopsy punch is so sharp, the edges of the biopsied site
will heal together quickly and leave only a very small scar that is completely
hidden by the hair coat.
2. Are there any complications of a skin biopsy?
Because a skin biopsy is such a simple procedure, complications are rare.
The most common is bleeding from the site after the dog is home. If this happens,
applying pressure to the site for a few minutes with gauze from your home
first aid kit should stop the bleeding. Some dogs will remove their own sutures
prematurely, and in these cases the site will have to heal on its own. This
will slow the healing process and may result in a slightly larger scar, but
even here, any scar is very hard to detect after the coat re-grows, even
in shortcoated breeds.
An unusual side effect of skin biopsies that we see occasionally and your
vet may mention, is that hairs may grow back a different color at the biopsy
site. Usually if the coat is light, the new hair will be darker. In dark or
black dogs, the re-growth may be white. Often the hair color will correct
itself but this may take some time.
Because the skin heals so well, skin biopsies do not need to be taken using
the same measures to ensure sterility as more invasive procedures. This means
the site does not need to be scrubbed vigorously prior to the biopsy, but
just gently cleaned with alcohol. Very rarely, perhaps one in several hundred
cases, an infection can develop at a biopsy site. If an infection occurs,
the biopsy site will feel hard, appear red and may drain. This will slow healing
and may result in a slightly larger scar at the site. If you think this is
occurring, contact your veterinarian, as antibiotics may be needed to clear
the infection.
Finally, veterinarians are always careful about the total amount of local
anesthetic injected. If given in excess, and if enough is absorbed into the
dog’s system, the anesthetic can depress the heart rate and induce seizures.
This is virtually never a problem in an adult dog, but must be kept in mind
on the rare occasions when many biopsies are taken from a small puppy.
3. How much of my dog’s show coat will have to be clipped in order to
perform the biopsy?
As we have discussed above, skin biopsies are not sterile procedures and
extensive and close clipping of the hair does not have to be done. In order
to maximize the cleanliness of the biopsy site, it is optimal to clip long
hair out of the way before taking the biopsies and if your dog is being biopsied
as part of a work-up for a skin disease, we would recommend allowing your
vet to clip the coat as much as they think necessary.
For dogs in show coat, biopsies can be taken with no or minimal clipping
at the biopsy site; however this will slightly increase the risk of infection,
as hair may be brought into the surgical site. We have found that some veterinarians
are willing to take punch biopsies for SA screening without clipping when
the dog is in full show coat. If this is important to you, this should be
discussed with your vet before taking the biopsy specimens.
The above information is simply informational.
It's intent is not to replace the advice of a veterinarian nor to assist
you in making a diagnosis of your pet. Please consult with your own veterinarian
for confirmation of any diagnosis. Your pets life may depend on it.
