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. 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
