Page 6 - Equine Matters - Autumn 2013

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C U S H I NG S D I S E A S E
Cushing’s disease
(PPID)
Cushing’s disease (also known as Pituitary Pars Intermedia Dysfunction
[PPID]) is the most common hormonal disease of older horses/ponies,
and up to 20% of animals over 15 years of age may have the disease
1
.
Younger horses and ponies may also develop Cushing’s as the disease
is gradual in onset, and recent data has demonstrated that Cushing’s
may be responsible for laminitis in a significant proportion of 10-15
year old animals
2
.
5
EQUINE MATTERS
The hypothalamus and pituitary gland,
which sit deep inside the skull at the
base of the equine brain, control the
production of many hormones responsible
for normal body functions - hormones
are the body’s chemical messengers.
In some horses and ponies, nerves
(neurones) in the hypothalamus undergo
degeneration and produce insufficient
quantities of a neurotransmitter substance
called dopamine.
Dopamine acts as an ‘off’ switch for the
pituitary gland. When the Pars Intermedia
of the pituitary gland is not exposed to
enough dopamine, the ultimate outcome
is the production of abnormally high levels
of hormones such as cortisol and ACTH.
We think that too much of these and other
similar hormones in the bloodstream lead
to the symptoms associated with the
disease. The Pars Intermedia itself also
becomes progressively larger as it works
hard to produce an increased amount of
hormones. Equine Cushing’s disease is
more correctly termed Equine Pituitary Pars
Intermedia Dysfunction or ‘PPID’.
Horses suffering from PPID can show a
range of clinical signs as the hormones
that are overproduced can affect several
areas of the body. Horses may show all,
some or only one of the symptoms if they
are affected, but as the disease is gradual
in onset they may develop more symptoms
as they get older
2
.
Laminitis could be considered the most
important symptom of PPID as it is such
a distressing, painful condition that can
end athletic function or even result in
euthanasia. Recent evidence shows that
laminitis is often the first clinical sign to
develop in younger horses
2
.
In addition to laminitis, another clinical
sign that is well recognised is the
development of an abnormal hair coat -
ranging from mild changes in coat
shedding right through to a full, long,
curly, overgrown coat (also known as
hirsuitism). As this happens gradually,
owners sometimes don’t notice that
their horse or pony’s haircoat is changing
and the normal shedding pattern
is altered.
What causes Cushing’s disease (PPID)?
The pituitary glands sits at the base of
the brain and controls the production
of hormones
Hirsuitism (a thick curly coat) is the
classic sign of PPID (Cushing’s) but signs
are often more subtle
Clinical signs
As well as laminitis and hirsutism,
other PPID indicators include:
l
loss of muscle condition, and/or a pot
bellied appearance
l
fat re-distribution such as fat pads over
the eyes
l
excessive or patchy sweating
l
lethargy and poor performance
l
increased drinking and urination
l
recurring infections that are hard to treat
(e.g. sinusitis or skin infections).
Laminitis could be considered one of the
most important symptoms of PPID
Anterior
Pituitary
Hypothalamus