Pruritus or itching is an unpleasant sensation
that causes a cat to scratch or bite at himself. It is caused
by chemical reactions that occur in the skin and stimulate the
nerves, causing the brain to feel the itch. In fact, the act
of scratching itself may stimulate these inflammatory
reactions in the skin and make the condition worse. Any skin
condition that causes inflammation can cause pruritus.
How pruritis affects your cat’s health depends on the degree
of the pruritus. Mild pruritus may hardly have any effect at
all. However, severe pruritis leads to intense scratching,
which may result in painful skin lesions that may become
infected.
Every cat has a threshold of pruritis or an
“itch threshold.” This is the point where all of the
sources of itching finally add up to enough irritation to
cause the irresistible urge to scratch. Scratching begins when
the stimulation exceeds that threshold. For example, a cat
with a mild allergy to house dust mites may be below the
threshold but may begin to scratch severely when he becomes
infested with fleas.
Pruritus is associated with other skin diseases, including
secondary bacterial skin infections (pyoderma) and secondary
yeast infections. But it is the main symptom of skin
conditions like allergies and skin parasites.
What To Watch For
Scratching or biting. If this continues beyond one day
and leads to lesions such as hair loss, reddening of the
skin and obvious pain or discomfort, have your cat
evaluated by your veterinarian.
Chronic licking of the feet. This is also a symptom of
pruritus.
In cats, pruritus may be subtler and may present as
excessive grooming. You may see thinning of the hair coat
where the cat is licking or raised, crusty lesions
(miliary dermatitis).
Diagnosis
Diagnostic tests may be needed to determine the cause of the
pruritus. Your veterinarian will probably do the following:
A complete and thorough medical history
A thorough physical examination
Skin scrapings to rule out mange mites and other
parasites
Fungal cultures of hair to rule out dermatophytes
(ringworm)
Treatment
The key to relief from pruritus is to identify and treat the
underlying cause. Pruritus may be temporarily relieved with
medication but the itching often recurs after the medication
is finished. Temporary relief may come from the following:
Antihistamines
Fatty acid supplements
Soothing shampoos
Corticosteroids
Home Care
At home your care will be aimed at preventing pruritis by
keeping your cat’s coat clean and brushed free of mats.
Consult with your veterinarian to establish a complete flea
control program. If your cat is being treated for pruritis,
administer all prescribed medication and follow all your
veterinarian’s instructions.
Related Diseases
Many skin diseases can cause or can contribute to pruritus.
Every cat has a threshold of pruritus. When the nerves of the
skin are stimulated by mediators of inflammation to a level
below that threshold, the cat will not scratch. Scratching
begins when the stimulation exceeds that threshold. It is
common to see cats with two or more skin conditions that cause
pruritus concurrently. For example, a cat with a mild allergy
to house dust mites may be below the threshold but may begin
to scratch severely when he becomes infested with fleas.
Allergic Skin Diseases
Flea allergy is the most common allergic skin disease in
the United States. Cats with flea allergy tend to scratch
their back ends leading to lesions on the rump, hind legs,
tail and belly. Since it takes just one flea to make the
cat react, the presence of fleas on the cat may be minimal
to absent.
Atopy is a reaction to airborne allergens such as
pollens, house dust, house dust mites and molds. Cats with
atopy tend to scratch their ears and face and tend to chew
and lick at their feet. The condition is often worse
during summer months when pollen and mold levels are
increased.
Food allergy is a reaction to one or more ingredients in
their food. These cats tend to scratch in the same places
as those with atopy.
Insect allergies (insect bite hypersensitivity) are less
common than other allergies. Lesions are evident in areas
where insects such as mosquitoes are likely to bite
(bridge of nose, ears).
Contact allergy is a reaction to an irritant that
touches the skin, often the belly or chest. Allergies of
this type are rare.
Parasitic Skin Diseases
Scabies is an intensely pruritic skin condition caused
by the sarcoptic mange mite. Lesions are seen on the ears,
elbows and hocks (ankles).
Demodectic mange is caused by the demodex mite. This is
usually a disease of young cats and causes dramatic hair
loss and dermatitis. This disease is often not pruritic,
but can lead to a secondary bacterial infection of the
skin (pyoderma) which may be itchy.
Fleas can cause pruritus in cats that are not flea
allergic, although the degree of pruritus is less severe.
Cheyletiellosis is an itchy skin condition caused by the
cheyletiella mite. Lesions are usually most dramatic along
the top of the back. These mites are sometimes visible to
the naked eye as small, moving, white specks, hence the
name “walking dandruff mite”.
Lice are small insects that are easily seen with the
naked eye that can cause pruritus.
Ear mites cause itching of the ears in cats and can
sometimes cause itching elsewhere on the body.
There are many other causes of pruritus, including
secondary bacterial skin infections (pyoderma) and secondary
yeast infections.
Diagnosis
The key to treating pruritus is to identify and treat the
underlying cause. Your veterinarian may want to perform a few
diagnostic tests to determine the cause of the pruritus. Tests
may include:
A complete medical history. A thorough medical history
is the foundation for the diagnosis of any dermatologic
condition. The breed of your cat, the age, onset of
symptoms, duration of symptoms, severity, season in which
the problem occurs and the response to previous
medications all are important clues.
A thorough physical examination. A complete general and
skin examination that includes the skin, ears, footpads
and claws is equally important. Unlike most organ systems
in the body, the skin can be directly observed. Therefore,
what your veterinarian sees is of value in establishing a
diagnosis. Your veterinarian will usually look for primary
lesions (those caused directly by the disease) and
secondary lesions (those caused by your cat's response to
the disease). The distribution of the lesions on your
cat's body is critical to diagnosis since animals tend to
scratch in certain areas with certain diseases. Also, a
flea comb is often used to look for fleas, flea dirt or
other parasites.
Skin scrapings. Skin scrapings are commonly done to
diagnose skin parasites. A scalpel blade is used to scrape
layers of skin that are then be examined under the
microscope for mange mites and other parasites.
Fungal cultures. Your veterinarian may do a culture of
the hair to rule out dermatophytes (ringworm). Although
not always pruritic, ringworm can sometimes cause animals
to scratch and can mimic other skin diseases. A small
amount of hair is plucked from a skin lesion, placed on
the growth media and incubated for 10 days to four weeks
to observe for growth.
Blood and allergy tests. Your veterinarian may elect to
do blood tests to assess other organs that may have an
effect on the skin, or allergy tests or food trails if
allergy is suspected.
Treatment
The only way to relieve pruritus long-term is to diagnose and
treat the underlying cause. Medications may be effective in
mild cases or may offer temporary relief for more severe cases
while waiting for the underlying cause to respond to
treatment. But the itching often recurs after the medication
is finished. Generally, treatment consists of the following:
Antihistamines. These drugs are much less helpful in
cats than they are in humans and will significantly help
only 25 to 30 percent of cases. Nevertheless, they are
often prescribed since they are relatively safe drugs when
compared to corticosteroids. Some cats respond better to
one antihistamine than another, so veterinarians may try
two or three different types before giving up on them.
Fatty acid supplements. These may help relieve pruritus
by modulating the immune response and may be helpful for
chronic pruritus. Certain fatty acids, such as
eicosapentanoic acid found in fish oils, help to change
the chemical composition of mediators produced during the
allergic response, thereby making them less inflammatory.
Like antihistamines, these products are not always helpful
but they are relatively safe. Some cats that do not
respond to antihistamines may do well with a combination
of antihistamines and fatty acids.
Shampoo therapy. Shampoos that contain colloidal oatmeal
are soothing, and because these shampoos are moisturizing,
they can be used frequently without drying the skin. Some
oatmeal-based shampoos contain topical anesthetics or
topical corticosteroids that are safe and further help in
reducing pruritus.
Corticosteroids. When other therapies are not effective,
corticosteroids such as prednisone may be prescribed.
Again, these drugs may help in some cases but are less
effective in others. Many side effects associated with
corticosteroids restrict their long-term use. Some of
these include increased thirst and hunger, which may lead
to obesity and suppression of the immune system, which may
lead to infections, irritation of the stomach and damage
to the liver or adrenal glands. Short-acting, oral
corticosteroids are much safer than long-acting
injectable, since they can be cleared from the body
rapidly should side effects occur.
Pruritus can be a frustrating problem because there are
many different causes and, therefore, many different
treatments. Thus, it is extremely important that you stay
in close communication with your veterinarian until the
problem is resolved. In addition, you should also do the
following:
Administer all medications as instructed.
Keep your cat’s coat clean and properly groomed.
Observe closely for fleas. Flea infestation makes any
pruritic problem worse. Consult with your veterinarian to
establish a complete flea control program.
Observe for the appearance of new rashes, areas of hair
loss or other new lesions that may indicate secondary
problems like pyoderma which could require additional
medication.
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