Discoid Lupus Erythematosus (DLE)
(also called DLE, Nasal Solar Dermatitis, or Collie Nose)
Lupus – What is this Disease?
Lupus is an immune-mediated disease stemming from your own immune system reacting against your own DNA. This in itself sounds like a recipe for disaster since almost every cell in a body has DNA in it, but it is important to remember that under normal circumstances your DNA is sequestered in a cell nucleus where the antibodies of the immune system cannot reach it. The immune-system in lupus is not going around attacking every cell in the body to get to its DNA; instead, the immune system only sees DNA after cells have died and their assorted broken parts are floating around as debris. The immune system reacts to this loose DNA and generates antibodies. These antibody:DNA complexes deposit in delicate membranes, such as the kidney filtration membranes, blood vessel linings, joint capsules, and other similar structures. Once caught in these membranes, other immunologic cells are attracted and further inflammatory damage results.
Systemic lupus (SLE) involves this kind of inflammatory disruption (called a Type III hypersensitivity reaction) and prognosis depends on which organ systems are affected and how severe the damage is. The disease is not curable but is manageable with immuno-suppressive drugs.
The name “lupus” stems from archaic times when the disease was thought to have been caused by the bite of a wolf.
Systemic Lupus Versus Discoid Lupus
When people use the term lupus, they are referring to systemic lupus, or SLE as described above. Discoid lupus is a form of lupus that is confined to the skin and is substantially more benign because of this confinement. Discoid lupus, or DLE, is almost exclusively a canine disease and is almost always limited to the leather of the nose, called the nasal planum.
DLE does not progress to SLE.
Features of Discoid Lupus (DLE)
Lesions of DLE are almost always limited to the nose though they can extend up the bridge of the nose and sometimes affect the ears or inside the mouth. Early signs of the condition start with loss of nose pigment. A black nose will become bluish-grey or even pink. Scaling and cracking of the skin results and eventually the nose will ulcerate. Exposure to sunshine makes the condition worse and there seems to be a genetic predisposition among the collie breeds (hence the term collie nose).
There are several other conditions that also cause crusts and/or erosions on the nose, so it is important to get the right diagnosis. Some other conditions to rule out include:
- Dermatophytosis (ringworm of the nose)
- Nasal pyoderma (Staph infection on the bridge of the nose)
- Pemphigus foliaceus (a different immune-mediated skin disease)
- Hyperkeratosis (a callusing disease of the nose)
- Nasal lymphoma (a type of cancer)
- VKH-like syndrome (another immune-mediated disease)
Diagnosis is by biopsy, which means a small piece of nose tissue must be harvested and sent to the laboratory for analysis. Most dogs will not hold still for this kind of a procedure on their nose so sedation is generally needed to get proper samples. Expect stitches afterwards; some mild bleeding is possible.
Discoid lupus is a condition with many treatment options depending on the severity of symptoms.
Avoid Strong Sunlight
Since this condition is made worse by the sun, it is important to avoid intense sunlight. Sunscreens have been advocated but it is important to realize that there are toxic ingredients in many human sunscreens and anything you apply to a dog’s nose will be licked off. Pet sunscreens are expected to be licked.
See the pet sun protector approved by the Food and Drug Administration and endorsed by the American Animal Hospital Association and the ASPCA.
The immune-suppressive effects of steroids are helpful in DLE but the systemic side effects are undesirable. Side effects are minimized by using topical steroids, typically starting twice a day and eventually dropping to an as needed basis for maintenance after the nose is healed.
Tetracycline is an antibiotic with immunomodulating properties separate from its antibiotic properties. Niacinamide (also called nicotinamide) is a B vitamin supplement related to niacin (vitamin B3). The combination of these two medications has been found effective in 70% of dogs with DLE though it can take up to two months to see an effect. Treatment is given three times daily, which is relatively inconvenient for most people so alternatives have been sought. Doxycycline can be used twice a day and is frequently substituted for tetracycline.
Oral steroids are often used to get the condition under control relatively quickly (within a month) and can be used after that as the sole therapy after the lowest effective maintenance dose is determined. Side effects include panting, excessive thirst and urination, and increased appetite, which are frequently not desirable so often steroids are used in conjunction with one of the other therapies that has a longer time to maximum effect with the idea of dropping back the steroids when the second therapy can take over.
0.1% Tacrolimus (Protopic®)
This topical immunomodulator is made for human use. It is effective for use in DLE and does not cause problems if licked. Only small amounts of ointment are needed and the tube should last a long time, which is good news since it is not inexpensive.
If your dog is diagnosed with discoid lupus, discuss therapy options with your veterinarian. If your dog has a crusty nose or ulcerated nose, expect a biopsy to be needed to sort out the diagnosis properly before treatment can be prescribed.
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