Hypertrophic osteodystrophy (HOD)

HOD Hypertrophic Osteodystrophy

Affects large breed dogs, is a painful orthopedic condition with fair to poor prognosis.

Breeds affected:
Rapidly growing large breed dogs
Two to six months of age is most common
Typical breeds affected Great Danes,Boxers, German shepherds, Weimaraners
Symptoms:
Fever, anorexia, depression
Lameness may vary from mild to severe
Reluctance to stand if multiple limbs affected
Lameness may be episodic and most dogs recover after one episode
Long bones mainly affected, painful to touch with swelling & hot to the touch
Other symptoms may be : diarrhea, discharge from the eyes, tonsillitis, thickening of the foot pads, pneumonia, and abnormal development of the enamel of the teeth.
Causes:
Currently unknown
Proposed causes:
distemper virus infection
vaccination with distemper virus
bacterial infection
other viral infection
Vitamin C deficiency is not likely as dogs make this vitamin in their liver.

Treatment
This is a self-limiting disease which can last a few weeks

  • Treatment is largely supportive
  • Intravenous fluid therapy
  • Pain medications
  • Anti-inflammatory medications
  • Antibiotics if bacterial infection is suspected
  • Dogs that are severely affected should be euthanatized

Prognosis
Prognosis is variable

  • Dogs having mild disease usually have a good prognosis
  • Dogs having severe disease have a poor prognosis
  • Permanent skeletal deformity can occur
  • Dogs usually do not die of the disease rather are euthanatized if recovery is poor or if clinical signs are severe
  • Recurrence can be a problem until the dog reaches maturity

more info:
http://www.vetsurgerycentral.com/hod.htm
http://www.vetinfo.com/dencyclopedia/dehod.html

U. C. Davis Update
For over 12 months, the Center for Companion Animal Health (CCAH), the Canine Health Foundation (AKC) and the Weimaraner Club of America have been developing an informative data base to investigate immune system disease in the Weimaraner breed. The aims of the data base at its inception were to identify major diseases within the breed, and to eventually use pedigree and DNA information on the data base to locate genetic markers for use in breed selection programs. In the design of the data base, we elected to use a “closed” format to facilitate identification of disease affected groups.

We have now worked with several pure-breed dog clubs, and the “closed” data base has been very useful during the early investigation of a disease, providing anonymity for the breeders submitting information, and thereby reflects more accurately the true status of the problem in the breed.Current Status of the Weimaraner Data Base
To date, there are over 850 Weimaraners entered into the data base, with several significant disease syndromes already recognized (Table 1).One of the major disease syndromes present in the Weimaraner breed is Hypertrophic Osteodystrophy, which causes pain and lameness associated with swelling of the growth plates in the long bones (e.g. femur, humerus). Other disease syndromes recognized include a post-vaccinal reaction with high fever and variable involvement of other body organs; the “classical” Immunodeficiency syndrome that has been recorded in the veterinary literature, with recurrent infections involving the bowel, skin, and urinary tract; hypothyroidism and mast cell tumors. Other less common diseases are also recorded on the data base, and information on their prevalence is available on request.

Hypertrophic Osteodystrophy (HOD)
HOD is a common disease of rapidly growing, large and giant breed purebred dogs. In a recent study looking at breed predilection for developmental bone diseases, breeds reported at increased risk included the Great Dane (190 x increased risk for HOD compared to mixed-breed dogs), the Boxer (18.4 x), the Irish Setter (14.3 x), and the German Shepherd (9.5 x) [Munjar, 1998]. The Weimaraner breed featured prominently, with a 21 fold greater risk of HOD occurrence compared to mixed breed dogs. An increased risk for HOD in the Weimaraner has been suggested in the veterinary literature, with a litter of four HOD-affected Weimaraner puppies (Grondelen, 1976), and a different litter of four affected puppies (Woodward, 1982) reported.

The CCAH data base currently has 30 Weimaraner puppies diagnosed with HOD. Most of these puppies have presented to veterinarians for acute onset of fever, with swelling present at growth zones of the long bones. Loss of appetite and lameness were present in all these dogs. Males and females were equally affected, and the age of onset of the disease is typically 8-16 weeks of life. We have noted an association with recent vaccination. Of the 30 HOD-affected dogs, 24 received a vaccination within 3-5 days of the onset of the disease. It is important to note, though that there were instances of HOD not associated with vaccination, so that the vaccination may be the trigger for disease expression on the susceptible genetic background.

Diagnosis of HOD relies on the typical history, clinical signs, and the presence of the characteristic radiographic findings showing changes at the growth plate of long bones. The cause of HOD remains unknown, with earlier speculations of vitamin C deficiency (Meier, 1957; Holmes, 1962) or over-nutrition (Riser, 1965) discounted in more recent times (Grondalen, 1976). There is mounting evidence that viral infection may be important in the disease., with Distemper virus detected in the growth plates of dogs with HOD (Mee, 1993). To date, we have not been able to identify a link to the Immunodeficiency disease of the Weimaraner related to low levels of blood antibody IgA or IgM.

Treatment of HOD in other breeds has traditionally relied on rest, non-steroidal anti-inflammatory drugs (such as aspirin), and opiate analgesics (such as butorphanol or fentanyl) as necessary. In most cases, the disease is self-limiting, and most dogs recover in several weeks. The disease in the Weimaraner is different. The Weimaraner breed is prone to a severe form of the disease, with disease progression in many dogs resulting in death without the proper treatment. Our current recommendation is for practitioners to rule out infectious causes for the fever, and in the presence of radiographic changes in growth plates consistent with HOD, to treat these dogs with corticosteroids. Prompt recognition of the disease, and appropriate treatment art the keys to a good outcome in this disease.

Mode of Inheritance of HOD in the Weimaraner
The mode of inheritance of HOD in the dog has not been reported, but there is an obvious breed predisposition suggesting that genetic factors play and important role. A useful index for influence of genetic factors in the disease is the heritability of a condition. Heritability varies from 0.0, in which there is not genetic influence, to 1.0, in which the effect is determined solely by genetics. Diseases with strong management influences (such as exposure to an infectious agent through communal grooming) are expected to have a low heritability, and response to selection against disease will be poor. The more appropriate course would be to identify the common theme, and altar the environment to prevent exposure to the cause of the disease.

A disease with a high heritability suggests that genetic factors are involved, and implies that a selection program against the disease will have and effect on the prevalence of the disease. Calculation of the heritability requires use of pedigrees, with accurate disease status indicated for as many dogs on the pedigree as possible. Preliminary work in our laboratory has found a high heritability for HOD in the Weimaraner of 0.68 (95% confidence interval of 0.65-0.71), suggesting that HOD in the Weimaraner may have a significant genetic component. It is very important to note that this value cannot be extrapolated to other breeds with HOD, as heritablity is only valid in the population from which it is measured. Other breed clubs will need to similarly calculate this value to gauge the likely success of an selection program against HOD.

We suspect that HOD in the Weimaraner is inherited as an autosomal recessive disease, although we still need more HOD-affected dogs to prove this. Some of the characteristics of an autosomal recessive disease that we are seeing in the Weimaraner with HOD include: 1) skipping of generations, and 2) mating of carriers results in the expected proportions of 25% affected, 50% carriers, and 25% unaffected (figure 1). Detection of carriers relies to date on test matings, which is definitely not the desired approach to long term control of the disease. Our data does not support and autosomal dominant mode of inheritance, nor do they support an X-linked (or sex-linked) mode of inheritance .

Importance of Carriers in Autosomal Recessive Disease
The success of any selection program in autosomal recessive diseases relies on accurate detection of animals carrying susceptibility genes (figure 2). In the best case scenario, the mating of an unsuspected carrier animal to an unaffected animal will still result in the production of 50% carriers in the progeny. This in effect maintains the susceptibility gene for the disease at high levels in the population, even if the disease is seen only sporadically when chance matings of two carriers occurs. We believe this is one of the difficulties in the control of HOD in the Weimaraner.

Weimaraners with HOD-susceptibility genes do not have any known phenotypic markers that permit identification, and to date the only way to detect these carriers has been by test matings. Detection of these carriers has also been hampered by use of modified vaccination protocols that are designed to prevent expression of HOD during the susceptible growth period. While it is important to look after the health of our puppies, this factor must be borne in mind when a selection program against HOD is to be implemented in the absence of a sensitive genetic marker. One of the aims of our group has been to locate a genetic marker for susceptibility to HOD, allowing for sensitive detection of these carriers, and thereby, design a suitable breeding program

Reprinted from the October 1998 issue of the Weimaraner Magazine.<