PANOSTEITIS
By Fred Lanting
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
SYMPTOMS AND
DIAGNOSIS
Clinical signs are
those that 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 also
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
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
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 that 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 that 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
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 older 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 “overnourished”. 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” diets (high protein,
especially) 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
that 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 that may be more serious.
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Copyright 2001 Fred Lanting, Canine Consulting. Mr.GSD@juno.com. All rights reserved. Please
view his site Real
GSD.
NOTE: A well-respected AKC
and Schaferhund Verein judge, Mr. Lanting has judged in more than a dozen
countries, including the prestigious FCI Asian Show hosted by Japan Kennel
Club, the Scottish Kennel Club, a Greyhound specialty in England, and
more. National Specialties: 1994 GSD
Club of America National; 1991 Tibetan Mastiff National; 1990 Shiba National;
Fila Brasileiro Nationals (several times), Dogo Argentino National, Pyrenean
Shepherd National. Numerous
Chinese Shar Pei and Australian Shepherd specialties; regional Anatolian
Shepherd specialty. Numerous GSD, Rottweiler, &
Boxer specialties worldwide. He
is also the author of several ‘must read’ books, including THE TOTAL GERMAN
SHEPHERD DOG, CANINE HIP DYSPLASIA, CANINE ORTHOPEDIC PROBLEMS. A former professional all-breed handler in
the US and Canada, he has lectured in over fifteen countries on
Gait-and-Structure (Analytical Approach), Canine Orthopedic Disorders, and
other topics, as well as being a Sr.
Conf. Judges Ass’n (SCJA) Institute instructor. WV Canine
College instructor & member, advisory board. His full Curriculum
Vitae is very impressive and we are
grateful to him for sharing that knowledge on this site.