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DESCRIPTION
One of the main reasons for a young dog to be "pulled" from
a show, or excused from the ring, is the sudden lameness of
a condition known as panosteitis, familiarly labelled "pano"
by many breeders. Of some 130+ breeds recognized by the American
Kennel Club and hundreds more by some other registries, a
dozen or so have been reported to be affected.
This mysterious disease causes sudden lameness in many younger
dogs, but its greatest potential may be in false diagnosis.
The disease has been given various names: hematogenic chronic
osteomyelitis, enostosis, long-bone disease, panosteitis,
and eosinophilic panosteitis. It was first described by Gratzl,
and by Baumann and Pommer in 1951 in Vienna. Since then it
has been reported in Sweden, Germany, Hungary, what was then
Yugoslavia, and the United States, yet there is not as much
information on this subject in the early scientific literature;
there was no reference in several texts on orthopedic diseases,
and Smith's otherwise comprehensive text on Veterinary Pathology
had but a brief note on enostosis as "a German Shepherd Dog
disease", "analogous to eosinophilic panosteitis". An obscure
Yugoslavian doctoral thesis dated 1961 led to a couple of
references, and a dogged search (pardon the pun) of the international
orthopedic literature finally turned up a 1970 study published
in the AVMA Journal. Personal contact with orthopedic and
radiology specialists brought the search to some work at Purdue.
SYMPTOMS AND DIAGNOSIS
Clinical signs are those which are obvious or apparent upon
gross examination of the entire dog, as opposed to microscopic
or other types of study. Symptoms are determined by means
which may include gait and motion analysis, and comparison
with other limbs by manipulation and palpation. In humans
such a case history would include a verbal report by the patient
of his complaint. Radiologic study involves the use of X-rays,
and histologic determination usually requires euthanasia and
dissection of the tissues involved (long bones). A similar
term, pathologic, also refers to laboratory findings of functional
and structural aspects of the disease. Fortunately, a knowledgeable
breeder can probably diagnose pano faster and cheaper than
can a vet, merely by knowing the breed and pinching in the
right places.
Panosteitis is probably a disease of the osteoblasts, which,
you will remember, are those bone cells that produce the organic
osteoid and matrix vesicles needed for ossification. It involves
a necrosis of fat cells in the marrow of long bones. It is
a generalized (pan-) inflammation (-itis) of certain bones
(os-). Specifically, it occurs in five of the long bones of
the appendicular skeleton: the humerus, radius, and ulna of
the foreleg, and the femur and tibia of the hind limb. It
has not been reported in the long but narrow fibula of the
lower rear leg. More often than not, the first sign is a sudden
lameness in one foreleg. Exhibitors have claimed it always
occurs between the closing date for entries and the day of
the show, after all arrangements and plans have been made,
but this is something that has not been substantiated by unbiased
scientific studies.
Intensity of discomfort varies not only with the progression
of the lesion in the individual, but with the difference in
pain threshold between one dog and another. It may be so minor
that one has to press and probe to elicit pain response, or
it may be so bad that the dog will whimper and refuse to put
any weight on the limb. The degree of pain is not closely
correlated with the stage as seen on the radiographs. While
lameness may sometimes be observed in only one limb, the disease
has been radiographically discovered in at least two bones
simultaneously in some 96% of affected dogs. Further, the
typical lameness-recovery cycle of one or two weeks will shift
from one leg to another, although there may actually be as
many as seven bones involved at any one time. Usually, an
upper arm will be affected first, followed by a femur or ulna,
and often the problem will appear in another bone in the original
limb or its partner. There may be a lapse of several weeks
between episodes, and more than one phase may be present in
the individual at any one time.
Partly because of the nature of the disease and the fact that
the owner is not likely to do any damage to his dog by withholding
treatment if it is indeed pano, this may be the easiest to
diagnose at home with fair reliability. If you can elicit
a definite pain response by pinching the suspected affected
bone in the middle of the shaft, it is most likely panosteitis.
If the pain is at the distal end of the long bone, it could
instead be HOD, in which case a trip to the vet is certainly
in order.
Computing this simple test with the breed predilection and
perhaps previous experience, the owner may save himself some
expense. If you have any doubt, though, be sure to ask the
doctor.
Whether it is very common for the same bone to be the site
of recurrence is not a matter of total agreement, although
too many owners report it to be so, to ignore that strong
anecdotal evidence. One study of 100 consecutive cases at
New York's Animal Medical Center concluded that "after a bone
has passed through all phases of the disease, it is unlikely
that it will be affected again", and reported only one incidence
of return to a previously-affected bone. Another study released
5 years later held that "recurrence in the same bone was most
frequently found in the radius, followed by the ulna...",
but mentioned a 6-month or more interval between episodes
in individual long bones.
Symptoms of panosteitis may be confused, by the novice or
the vet with limited experience, with OCD of the shoulder
or one of the elbow dysplasias; if in the rear limb, it could
make someone think the dog has HD or cruciate ligament injury.
A case history plus information on the breed, family, and
diet can give some diagnostic clues. UAP, for example, is
often brought to light via trauma such as jumping off a ledge,
but pano shows up regardless of traumatic occurrences. The
most reliable and definitive diagnosis might possibly be by
a series of radiographs which can show the early, middle,
and late phases of the disease, but even then radiographic
signs can be so minimal that they can be missed, even if the
animal exhibits clinical signs and a number of films are correctly
exposed. Radiographs in both major studies were taken every
month from 5 to 30 months of age. This type of approach is
not feasible for the typical dog owner, nor is it necessary
or best in most cases, if experience is sufficient.
I find my own diagnostic method to be at least as reliable
as a series of radiographs: first, I take into account the
breed, and the second thing is to watch the dog walk, as other
problems can give subtle differences in gait. Since I have
long bred GSDs, and the disorder was once known as "that German
Shepherd Dog disease", I have had much opportunity to witness
its appearance in dogs of my colleagues. As soon as my 1981
HD book was printed, and I had said that I had never had a
dog with pano, I found the worst case I had ever encountered,
in one of my own dogs! By then, I had already plenty of practice
in palpation (feeling) diagnosis as a part-time professional
handler and consultant to other breeders. The third and most
reliable physical test is to pinch the dog in the middle of
the shaft of each of those ten bones (all the long leg bones
except the fibula) and compare its reaction, bone to bone.
Almost always, the dog will yelp with pain if you pinch the
affected bone in the limb it has been favoring. Try to squeeze
where there is very little muscle covering the bone, but only
in the middle, not at the ends. Pain upon pinching near the
joints can possibly lead you to suspect HOD or joint disorders,
but possibly other than bone cancer there is nothing that
gives the same response to pinching the middle of the diaphysis
(shaft) as pano does.
THREE PHASES
The first stage, the one most associated with acute pain,
exhibits the least evidence of the lesion's presence in radiographs.
There is some blurring, and an accentuation of the pattern
of fibrous bands extending from the cortex (the hard, denser
portion of the bone) inward toward the center of the medullary
canal, where the marrow is located. Film contrast between
the canal and cortex is diminished, and the radiodensities
of the medulla and its lining are slightly greater. The fatty
connective tissue takes on an appearance similar to eosinophilic
granulomas (hence one of the early names for the disease)
and bone is added to those fibrous bands, called trabeculae.
The great deal of congestion in the medullary canal is almost
undoubtedly the main reason for so much pain; if the poor
dog could reason, he might imagine his bones were about to
burst from the increased pressure! If a hole is drilled (a
punch biopsy) for the purpose of testing some of the marrow,
pain is abruptly diminished.
The second phase is easily diagnosed in the clinic by the
appearance of radiodense, mottled medullary tissue, beginning
in the vicinity of the nutrient foramen, that hole in the
side of the bone where blood vessels enter and leave. In pano's
second phase, the borders of this hole are characteristically
accentuated, the cortex appears less dense, and its inner
lining becomes less roughened. In cases where the medullae
are greatly affected, a remodeling (new bone cell formation)
takes place as a secondary response on the cortex's outer
layer, the periosteum, and it grows to several millimeters
thick. This is the swelling or inflammation of bone that gives
panosteitis its name. In 6 to 8 weeks these characteristics
gradually merge into the third phase.
During the approach of the third phase, the fibrous bone which
formed in the medulla is resorbed, giving the radiologist
a more normal picture again, and production of blood by the
marrow resumes a more normal procedure. It may take several
months for the bone to regain normal shape and appearance,
especially if pano had struck in the more mature youngster,
but it generally does heal satisfactorily. Only a radiology
specialist or a general practitioner especially well-trained
in this field will be able to tell later on if a particular
patient had had pano.
Interestingly, no fractures accompanying or following panosteitis
which could be considered related have been reported, despite
temporary changes in the porosity and density of these organs
as found in histo-pathologic examinations of euthanized dogs.
Perhaps this is due to the dog's extreme reluctance to put
weight on the afflicted limb during the first two phases.
Nor was there any evidence of acute infection or chronic (lasting)
inflammation. The disease and recovery reach a point of cessation,
with some evidence of its having been there observable upon
dissection and microscopic examination of the tissues. A little
of the marrow typically seems to be permanently replaced by
fibrous connective
tissue rather than bone, and the thickening of the outer surface
gradually returns to normal.
SIMILAR DISORDERS AND SYMPTOMS
You have seen that the differential diagnosis which the owner
can make with fairly good accuracy (pinching the bone) will
distinguish panosteitis from HOD and other disorders; the
vet can confirm it with radiographs and examination. Another
disorder which can give x-ray pictures very similar to the
"milky" or "cloudy" appearance of panosteitis is erythrocyte
pyruvate kinase (PK) deficiency. Some years ago, a screening
program to eliminate this hereditary enzyme metabolism disorder
in Basenjis was thought to have been successful, but around
1990, a few more were diagnosed. The osteosclerosis, an abnormal
increased density of bone, is apparently a pleiotropic effect
of the homozygous presence of the deficiency gene. Pleiotropy
means one gene (or identical gene pair, if recessive) gives
rise to more than one disease or characteristic; Alaskan Malamute
dwarfism/anemic blood disorder is another example. In the
Basenji disorder, the bone density that could take as much
as two years to develop might be one of the evidences of the
genetic problem, but only if accompanied by other tests.
Even then, it might be missed, as some affected dogs will
show normally high erythrocyte PK activity at the time of
the tests. But if some of the other symptoms are looked for,
the diagnosis is easier. Affected dogs often have heart murmurs,
atrophied muscles, progressive anemia, stunted growth, rapid
heartbeats, and swollen livers, hearts, and spleens.
HEMOPHILIA WITH SIGNS OF PANOSTEITIS
Some dogs have shown such frank signs of panosteitis that
a tentative but fairly strong diagnosis of pano has been made,
and then upon further tests run because of additional symptoms,
they were found to have Hemophilia A. Of course, it is possible
that some dogs can have both disorders at once, but based
on the incidences of the two, the coincidental appearance
might be hard to imagine except in certain isolated GSD families.
Dr. Jean Dodd, a noted blood specialist, has seen some notable
connection between pano and von Willebrand's Disease (vWD),
a different type of hemophilia. I think that probably the
signs of pano or the actual development of enostosis, as some
prefer to call it, in the hemophiliac dog come about via bleeding
in the marrow with osteoblast (bone depositing cells) activity.
CAUSE OF PANOSTEITIS
The cause or etiology is unknown, but fortunately the disease
is self-limiting: it follows a progressive pattern and generally
the animal recovers with or without treatment to a normal
state or one so close that you might not be able to tell it
had occurred without cutting the bones for microscopic examination.
In worse cases, some permanent scarring can be identified
by those especially adept at reading the radiographs for this
lesion. Since panosteitis is a disease of the fatty bone marrow
in the long leg bones of the adolescent or young adult dog,
it may be that research on bone marrow will lead to an understanding
of the etiology and hence the best treatments, cure, and prevention
of the disease.
Panosteitis was originally designated as hematogenic chronic
osteomyelitis associated with fever and infection. Later work
indicated these conditions, when present, were coincidental
rather than causative.
As mentioned earlier, infection is generally not associated,
and malignancy is likewise absent. Only one of the 100 dogs
in the Animal Medical Center study had tonsillitis (the tonsils
are "traps" for infectious agents circulating throughout the
body). Whenever vaccines, flea powders, worm medicine, diet,
and other environmental factors have been implicated, rechecking
has found that the only common denominator was physiological
stress. Bacteriologic cultures of marrow, and the histologic
examinations, rule out bacterial agents. White blood cell
and eosinophil counts were within normal in nearly all cases,
the rare exceptions being no doubt a result of some co-existing
but unrelated problem. An eosinophil, by the way, is a type
of cell of the peripheral blood or bone marrow, and a high
level is an indication of some sort of infection or attack
by parasites.
TRANSMISSION
In an experiment to discover possible genetic, infectious,
or contagious modes of transmittal, German Shepherd Dogs with
a history of panosteitis were crossed with Pointers from a
family in which it had not been observed. Also, purebred Pointers
and German Shepherd Dogs were kennelled side-by-side separated
only by a wire fence, and pups of both breeds were raised
together in the same pen. Regardless of contact, the Pointers
remained free of the disease while the Shepherds routinely
developed it. The crossbreeding results were inconclusive,
even though only one incident of panosteitis showed up as
late as the fourth generation of back-crossing the female
crossbreds to male German Shepherd Dogs.
Panosteitis does not appear to be related in any way to other
radiographically similar diseases. It has no bearing on, nor
is it affected by, other bone or joint diseases such as hip
dysplasia or the various manifestations of osteochondrosis.
Although radiographically panosteitis resembles some human
bone conditions, there is no real counterpart in man.
It has previously been thought that nutrition might not have
anything to do with the lesion, despite it occurring mostly
in large, fast-growing breeds. Calcium intake did not seem
to have any bearing on it, as evidenced in bone healing studies.
However, more testimonial evidence has since been mounting
among "breeders and feeders" that diet can indeed make it
much worse or more likely to appear in families predisposed
to it. When I was preparing the article on panosteitis for
the AKC Gazette, I undertook a review of my first 140 German
Shepherd Dogs, and until my 1981 book was in publication,
I had encountered only one case of panosteitis in the bloodlines
I was using and developing. It happened seven months after
the dog was sold to a home where his diet was considerably
"richer" than the balanced commercial dry dog food he was
used to. Clinical symptoms ended about ten days after onset,
and we really don't know if the administration of prednisone
had anything to do with alleviating it (cause and effect relationship
with this corticosteroid on pano not established), but no
further episodes occurred. It was some time later that one
of my pups at home developed the worst case I have personally
encountered, and I did not record what diet we had been using
about that time, but he was produced by a different sire than
any of my other dogs.
A question of nutritional impact on the disease can be raised
when comparing the dog's change in diet with the predominant
diet of those in the 100-dog study: raw or cooked beef, eggs,
cereal, and milk. Perhaps most of those 100 patients were
from "pet homes" where a dog is more likely to have been "over
nourished". There are other question which can only be
answered through research, but there is no current active
project regarding the cause and environmental control of panosteitis.
From personal experience as well as speaking with scores of
breeders, I am almost totally convinced that those dogs with
breed and/or family susceptibility for pano, who are fed very
"rich" (high protein, especially) diets are the ones most
likely to come up limping with the disorder. One after another,
people have told me that by going to a lower-protein but still
highly-digestible food, and not feeding very liberally, they
have stopped the course of pano in their kennels.
BREED, AGE, AND SEX CORRELATION
When first described, one of the names given the disease was
"chronic osteomyelitis of young German Shepherd Dogs", but
as it was studied in subsequent years, other breeds were found
to be affected, including the Rottweiler, Airedale, Irish
Setter, German Shorthaired Pointer, Doberman Pinscher, Great
Dane, Basset Hound, and Saint Bernard. One observer has seen
panosteitis in all of the better-known large and giant breeds,
but it has also been found in the Miniature Schnauzer, the
Scottish Terrier, and the Beagle.
The apparent prevalence in the German Shepherd Dog may partly
be due to the large population of this breed (worldwide, it
is number one), though we cannot overlook the very strong
genetic aspect. Clinics such as the one in which the data
on 100 consecutive cases were collected have a preponderance
of GSDs as patients. Body size is correlated with the number
of cases seen in a veterinary hospital or educational institution.
Growth rate is a possible factor, as it seems to be with HD.
Most of the large and giant breeds have a rapid early growth
pattern, though the commonalities of growth rate and large
size with panosteitis may not be as closely related as they
are with HD. If breeds such as the Dobe and Collie, with their
relatively flatter growth rate curve continue to have low
incidence of pano in relation to their populations, it still
might not be conclusive evidence of cause-and-effect, but
may point to a connection.
If one subtracts the extremes of a very few diagnosed after
full maturity, the curve of ages at time of episodes rises
from about 5 months to a peak around 10 months, and rapidly
diminishes, with very few cases after 18 months of age. In
the one study mentioned earlier the extraordinary number (10)
found at age 24 months may not be representative. The first
German Shepherd Dog to win Best In Show at Westminster, Covy-Tucker
Hill's Manhattan, reportedly had at least one episode of pano
at 4 years of age, but this was not documented.
There is a nearly 4:1 ratio of males to females affected by
panosteitis; the clinical signs are more severe and the disease
more nearly chronic in males. This echoes a pattern seen elsewhere.
Early in the U.S. space program it was discovered that women
could withstand the stress of G-forces (acceleration) better
than men. The U.S. Army determined that female dogs can run
26% longer and swim 46% longer than males. Bitches lead many
racing teams of sled dogs because they can run smoother and
calmer, some racing enthusiasts claim. And females are much
less prone to non-specific lameness (presumably this included
pano) according to the records of Zero (racing) Kennel. It
appears the stress of estrus (bitch's season is her highest
stress period) or pregnancy contributes somewhat to susceptibility.
TREATMENT
A great number of treatments have been proposed and tried,
but all have had very limited or extremely questionable success,
and then only as partial palliatives; nothing has been conclusively
shown to have a cause-and-effect relationship.. Since the
cause is unknown, treatment is indicated and routinely prescribed
only for the symptoms. Aspirin, sulfa compounds, other antibiotics,
vitamin C, prednisolone or similar steroids, and calcium supplements
have been most commonly attempted. Of the analgesics and other
medications tried, buffered aspirin (less irritating to the
canine digestive tract) probably has the greatest effect and
widest application in relieving some pain in some dogs. It
and the corticosteroids have the largest number of proponents,
but it has been my observation that most dogs with panosteitis
do not respond to these anymore than they do to anything else.
Corticosteroids do have an anti-inflammatory action and can
give remarkable relief in many ailments (and by some reports
do a little good in alleviating some pain in pano), but as
in the case of all drugs and foreign substances, there are
cautions. Prolonged or excessive use of aspirin can cause
stomach bleeding in dogs; steroids can bring on cardiovascular
problems including ruptured capillaries, and can damage the
immune system at least temporarily. If you decide to try a
pain reliever in spite of my advice, if there is overwhelming
compunction to do something, make sure you discuss with your
veterinarian the possible side effects and contraindications.
For every "cure" or "successful" treatment, you can find a
score or more cases in which it did not work at all.
One orthopedist said to me, "It's sort of like treating a
cold in a human patient where, if you give medicine it takes
about seven days to get over it, and if you do nothing it
takes about a week." In the case of this disease, however,
it may take anywhere from 2 days to 7 weeks for the pain to
leave one site with 1 to 2 weeks quite common.
Radiologically and histologically, it can be 2 months between
onset and the beginning of the late phase, and then several
more months before cortex and endosteum (inner lining of the
marrow cavity) regain normal appearance. It may take considerably
longer for the disease to run its course in all the bones
which may become affected. I have observed that most cases
are outgrown by age 18 months to 2 years, with most initial
episodes coming around 8 to 10 months of age; in many dogs
the disease will strike at a much later age than in others.
It is rarely a chronic situation in regard to pain; in most
cases symptoms appear only intermittently in many bones, and
many dogs will have but one episode in one bone.
Many of us experienced breeders believe that nothing you do
will likely make a fig's worth of difference in either pain
relief or remission. One private practitioner with much experience
in orthopedic disorders claimed that Zyloprime relieved clinical
and radiographic symptoms within 5 days, but we know that
many cases self-resolve in that period of time anyway, and
the experiments were not duplicated elsewhere. It appears
that nothing gives completely satisfactory results, so the
best course of action is no action at all; let the dog decide
how much weight to put on the limb and just wait. Perhaps
the best treatment regimen for dogs with pano is in the nursery
rhyme, "Leave them alone, and they'll come home, wagging their
tails behind them." It may be best to let the dog restrict
his exercise by himself, give him emotional support so he
doesn't go without food to the extent of exposing himself
to diseases or stresses he can't handle, and simply wait it
out.
CONCLUSIONS
In summary, panosteitis is a self-limiting disease affecting
many of the long leg bones, predominately in large dogs between
5 and 18 months old.
It is apparently unrelated to other lesions of the skeletal
or blood systems, and occurs only in the canine, more in some
breeds than others. Cause is unknown, but high-protein diets
may make symptoms worse or last longer. Panosteitis is "self-limiting",
i.e., it will "go away" whether one treats it or not. Since
afflicted dogs "outgrow" the disease with little or no expense,
it is unlikely much research funding will become available
to study it. The dog owner should consult his veterinarian
to rule out other problems which may be more serious.
Copyright Fred Lanting, Canine Consulting.
Mr.GSD@juno.com
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