What
are Cushing's Disease (ECD) and Insulin Resistance (IR)?
ECD is a disease that affects the pituitary gland.
It is often caused by a tumor in the pituitary gland, but
not always. The main sign of ECD is the increase of
Cortisol in the blood. The production of Cortisol is
produced in the adrenal gland. Why does the
body begin to overproduce Cortisol? Cortisol is
a hormone that is commonly produced by the adrenal gland
during times of stress (otherwise known as excitement,
fear, pain, trauma, exercise, and transport, to name a
few). In the case of ECD, there is an abnormally
high level of Cortisol in the body. It is typically
caused by the over production of ATCH, a hormone produced
by the pituitary gland. Why is this a concern?
High levels of cortisol are a concern because they can
impair the immune system functions, cause resistance
to insulin, impare the ability to use protein in the body,
and cause electrolyte abnormalities.
There is also a condition in conjunction with ECD called
precushings. This is where a horse may have some of
the symptoms of ECD, but ECD cannot be confirmed with
testing.
IR is is similar to type 2 diabetes in people. It is
a condition where the cells in the body cannot respond to
insulin the way they should. Insulin is a hormone
produced in the pancreas that allows the body to take in
glucose from dietary carbohydrates and proteins (amino
acids). This is necessary to manufacture enzymes,
cell structures, and muscle. When glucose and and
proteins are not taken in correctly, the body produces
more insulin than normal to try to correct the situation.
IR can be seen with ECD, but it can also be seen in
conjunction with hypothyroidism.
What
is the difference between ECD and IR?
The difference in ECD and IR can be found when you look at
the bloodwork that your vet will take when your horse is
diagnosed. You must look at the ACTH, serum
insulin, and glucose. Remember, IR can be
present without ECD and vice versa.
In an ECD horse there is an elevated ACTH level in the
blood. If the ACTH level remains high for too long,
it results in an elevated level of Cortisol. This
cortisol is what causes IR in horses with ECD.
Cortisol causes the insulin to not work quite right.
In IR without ECD, we find that the insulin is elevated
while the ACTH level is in the normal range. The
high levels of insulin in the body cause chemical and
vascular changes in the body which can lead to laminitis.
What
are the symptoms of ECD and IR?
ECD
Symptoms:
1. Abnormal
hair coat (longer than normal, often curly)
that does not
shed
out normally in the spring.
2. Mammary
enlargement and/or milk production in
some mares
3. Fatty sheath and/or heavy sheath secretions in
some geldings
4. Any or all of the symptoms listed below for
insulin
resistance and/or hypothyroidism
IR
Symptoms:
1. Easy weight gain
2. Abnormal
fat desposits
such as a cresty neck or
lumpy, cellulite-like fat at the tail base. These
fat
deposits will usually persist even if the horse loses
weight elsewhere on his body
3. Puffiness
(fat) in the hollows above the eyes
4. History of laminitis – commonly induced by
grass
5. Advanced symptoms include increased thirst and
urination, loss of body condition, especially muscle,
weakness, low energy
levels
Symptoms
of Hypothyroidism:
1. symptoms are VERY nonspecific and many overlap
considerably with those of insulin resistance.
2. Slow
shedding/longer than normal coat may be seen.
3. Energy
levels poor, exercise tolerance poor.
4. Horse
may be irritable and sensitive to touch.
5. Cannot
be diagnosed with any certainty by
symptoms alone. Need to do blood tests.
Symptoms
of Laminitis:
These vary greatly depending on the severity of the
laminitis. From
least severe to most they include:
1.
Less
spontaneous activity
2. Less
spontaneous trotting/cantering
3. “Depression”
4.
Reluctance to turn (puts more weight on one foot)
5. Reluctance
to move forward when lead
6. Lying
down more than normal (when pain severe, stay down most of
the time)
7. Standing
with the front feet further in front of the body than
normal and the hind feet further under the body than
normal
8.
Stiffness in the shoulder muscles
9. Buckling at the knee
10. Refusal
to move
11. Hind
end muscles tightly bunched up (shifting most of their
weight to the hindquarters)
Examination
of the feet may show (usually worst in front feet):
1. Feet
feel warmer/hotter than usual
2.
Pulses in the arteries running over the sesamoid bones at
the back of the ankle are very strong and pounding
3.
Puffiness or redness at the coronary band
4.
Pain on sole pressure about ¼ to ½ inch in front of the point of the frog
5.
A bruised appearance to the sole
6.
Red or black discoloration of the white line
7.
Widening of the white line
8. Appearance of rings on the feet that are close
together at the toe but
get progressively wider over
the quarters and heels
How
can ECD and IR be diagnosed?
There are several ways that ECD and IR can be diagnosed.
All of them are tests done by your vet.
1. Blood ACTH: This is the test that is
typically used to diagnose ECD. Remember the ACTH level can be elevated due to stress, but
not nearly as
high as the levels of ACTH in a horse with ECD.
2. Cortisol Rhythm Test: This is a screening
test for ECD. Unfortunately this
test can show false positives and false negatives.
The rate of false
positives is approximately 35%. This test involves
sampling the blood
twice in one day. Once in the am and once in the pm.
3. Dexamethasone Suppression Test: This is
another type of screening test. It involves the injection of drug dexamethasone into the
horse. There will
then be a collection of blood samples in either an 8 or 12
hour period. This test can potentially increase the risk of causing or
worsening laminitis. There is a potential for false positives and negatives,
but this test is felt to
diagnostic by some veterinarians.
4. TRH Stimulation Test: This test involves
the injection of TRH into a horse. The TRH causes a spike in cortisol in a horse with a
pituitary tumor. Samples are drawn between 15 and 30 minutes after TRH is
injected. This is
probably highly diagnostic for ECD.
5. Combined TRH test and Desamethosone test:
Involves both tests described above.
6. Urinary Cortisol Creatinine Ratio: This is a test
of the cortisol levels in urine. This test is not 100% diagnostic, but it is
highly suggestive because it
is more accurate than blood cortisol levels in determining
increased production of cortisol.
7. Blood Insulin Test: A test that shows the
levels of insulin in the blood.
8. T4 and T3 Test: These tests measure the
function of the Thyroid.
9. Chemistry Screen: This screening checks for
organ function, dehydration,
blood sugar, and electrolyte abnormalities. This
test should be used in
conjunction with testing for blood cholesteroland
triglyceride levels for ECD
and IR horses.
Care and
Management of ECD and IR can be easy. If your horse
has ECD, he or she may need a prescription medication, but
it may also be controlled by an herbal supplement,
depending on the severity of the ECD. You need to
determine the right diet for your horse and be able to
balance it properly. If you plan to feed hay from a
local distributor, you will need to have each bale of hay
analyzed to determine the NCS (nonstructural carbohydrate
level- this is primarily the sugars in the hay.) You
will want to use grass hay only with Timothy or Timothy
mixed with Orchard grass being your best choice. You
may also choose to add beet pulp that does not have
molasses to the hay. This is in replacement of all
grain!
You will
also want to examine the minerals in your hay to determine
what supplements that it needs added to be balanced.
One supplement that can help tremendously is Chasteberry.
It comes either in powder form or berry form (the berry
form will need to be ground.) for more information
on feeding a horse with ECD or IR, please see the website http://pets.groups.yahoo.com/group/EquineCushings/.
On this website you can find an emergency diet for a horse
with ECD or IR as well as information on feeds,
information on distributors in your area, a glossary of
abbrevations and terms, and most importantly you will be
able to get advice from one of the leading authorities on
ECD and IR, Dr. Eleanor Kellon, DMV. Please
join the list and take a moment to read through all the
starting files, fill out a Case history for your horse, and
then post to the group for information and support as you
begin the process to help your horse live and flourish
despite one of these diseases.
If you
have a horse diagnosed with ECD or IR and have trouble
finding a feed store in your area that is willing to carry
the products that you need for your horse, feel free
to email me and I will give you a copy of the letter that
I am sending to my feed stores. This letter is my
way to help educate the owners and buyers at the feed
stores on ECD and IR. It gives them statistics on the
numbers of horses that could possibly be diagnosed with
ECD and IR (to show the amount of business they can
gain by carrying the products needed), a list of products
that can be used by horses with ECD and IR, a description
of the diseases and their symptoms, and an understanding
that these products do not need to be used solely by
horses with ECD or IR, but also for horses that do not
have these diseases, but could possibly be predisposed for
these diseases. You cannot predict what horses get
these diseases, but you can begin balancing a horse's diet
early in an effort to limit the side effects of thse
diseases.
Examples
of products that might be used for horses with ECD and IR
(please be sure to check labelling for the NSC level and
the guaranteed analysis):
Ontario
Dehy Timothy Balanced Hay Cubes
Beet Pulp
without Molasses
Chasteberry
Pwder or Berries
Blue Seal
Hunter
Blue Seal
Carb Guard
Poullin
Carb Safe Complete
Sterett
Low NSC Pellets (aka Mid Valley Milling)
Buckeye
Safe and Easy
Brandi Qualset - 2007 |