Hypertrophic osteodystrophy in dogs – HOD in puppies

Overview

A systemic disease of growing dogs involving bone pain

HOD affects the metaphyses of long bones: the bone regions near the growth plates. Among 39 dogs studied, 24, or 61.5%, had lesions in the lower radius, near the wrist. The lower ulna was also affected in 24 dogs, or 61.5%. The lower tibia was affected in 12 dogs, or 30.7%. Other bones can nevertheless be involved, such as the humerus, ribs or lower jaw.

HOD is a rare disease occurring particularly in growing large dogs. Recovery from mild HOD can be complete. Severe disease, however, can permanently affect limb growth. Fever and poor general condition are possible features.

Different from rickets or panosteitis

Rickets can result from calcium or phosphorus deficiency or an incorrect dietary balance between them. In panosteitis, pain relates to changes within a long bone and can shift between limbs. The findings and treatment principles of these diseases differ from HOD.

Causes

Disturbed blood flow and bone formation

The exact cause of HOD is unknown. Its development involves reduced blood flow to the bone's growth region. This disrupts ossification and can cause death of bone trabeculae. An inflammatory response develops in the damaged area. This partly explains why the growth region is swollen and painful.

The number of bone-resorbing cells, called osteoclasts, may increase in the inflamed area.

Inflammatory susceptibility and inheritance

An inherited predisposition is suspected particularly in Weimaraners. An abnormal inflammatory response is also considered a possible underlying mechanism. Bone lesions have been described as sterile inflammation, with inflammatory cells accumulating in bone tissue. Sterile here means that the inflammation itself does not establish bacterial infection.

A causal relationship between HOD and vaccination has not been consistently confirmed. Puppy vaccinations and the usual onset of HOD occur at the same life stage. Vitamin C deficiency is not considered a proven explanation for HOD. HOD is therefore not directly equated with a bone disease caused by vitamin deficiency.

Risk factors

The usual age at onset is around 2–8 months, during rapid puppy growth. The disease has nevertheless been described in small and medium-sized breeds and dogs as old as 15 months. Breeds described as predisposed include Great Danes, Weimaraners, German Shepherd Dogs and Irish Setters. Large size is therefore not an absolute diagnostic requirement.

In a group of 39 referral patients, the median age at onset was 14 weeks. Ages ranged from 8–32 weeks. Several studies included more males, but a definite sex predisposition has not been established. Affected littermates have been identified particularly in Weimaraners.

Typical symptoms

Pain and swelling are often bilateral and fairly symmetrical. The area around swollen bone may feel warm. You may notice:

• Lameness, which may be particularly obvious in the forelimbs.
• Limb swelling near joints.
• Tenderness or yelping when a limb is touched.
• Reluctance to get up, walk or join in play.
• Fever and being more tired than usual.
• Reduced appetite or refusal to eat.
• Diarrhoea, which can start before visible lameness.

Pain can sometimes occur on mouth opening or handling the spine. Signs may settle for a time and later return.

Among the 39 dogs studied, 34, or 87.2%, had a recorded fever. Seventeen patients, or 43.6%, were unable to walk.

Complications and consequences

Growth disturbances and severe systemic illness

A growth plate can be permanently damaged, causing a limb to grow at an abnormal angle. Severe disease can impair later walking, running and play. Concurrent problems such as pneumonia can complicate treatment. In the worst cases, pain and deterioration may lead to a decision to euthanise.

Recurrence of signs

Among 25 dogs followed up, 8, or 32.0%, had recurrent signs during growth. The median time to recurrence was 50 days after the original diagnosis. The range was 7–212 days. Suspected recurrence was not, however, always confirmed with new images.

Four of the 25 dogs, or 16.0%, later developed a disease considered immune-mediated. It is not yet known whether dogs with HOD have a greater risk of later immune diseases than other dogs.

Diagnosis at the vet

Clinical examination and bone imaging

Your vet assesses age, breed, signs and findings from skeletal examination. Pain and swelling in long-bone growth regions direct suspicion towards HOD. X-rays are usually the first imaging test. Images are checked for a darker line in the growth region running parallel to the growth plate. This finding is called the double physis sign.

Denser bone, or sclerosis, may be visible beside the area of bone destruction. New bone may later form around the bone. A chronic lesion can resemble thickening of the bone cortex. Imaging appearance therefore depends on the disease stage.

When are other tests needed?

Blood and urine tests investigate concurrent problems requiring treatment. CRP, an inflammatory marker, may be raised with a systemic inflammatory response. Bone changes must also be assessed against the possibility of bacterial osteomyelitis. A bilateral, symmetrical limb pattern supports suspicion of HOD.

CT can complement investigations if signs are vague or X-ray findings very subtle. It distinguishes structures without the overlap occurring on X-rays. CT is nevertheless not needed for every typical HOD case because X-rays are the first imaging test.

Hereditary trapped neutrophil syndrome in Border Collies can involve HOD-like bone changes. The Irish Setter's hereditary canine leucocyte adhesion deficiency, or CLAD, can also cause similar skeletal findings. CT performed for another reason, such as investigating fever, can reveal typical lesions in limb portions included in the scan.

A new episode is reassessed

Returning pain during growth may fit HOD recurrence. New X-rays can confirm bone changes and rule out similar diseases where necessary. Immune-mediated polyarthritis, for example, can cause signs resembling recurrence. A new episode of lameness is therefore not automatically considered another episode of the same disease.

Treatment

Pain relief and control of inflammation

HOD treatment aims to control signs and relieve pain. Your vet may use an NSAID or other pain medication according to the situation. An anti-inflammatory corticosteroid is selected for some dogs. Medication is chosen using examination results and the dog's general condition.

In Weimaraners, corticosteroids may produce a better response than NSAIDs. The best shared treatment approach for every breed has not, however, been established. Response is monitored through pain, movement and general condition. Do not change doses or stop medicines on your own initiative: the treating vet directs medication.

Hospital care and nutrition

Severe pain may require stronger pain relief in hospital. Fluids support a puppy unable to eat and drink enough. Nutrition is maintained through a feeding tube where needed. Concurrent diarrhoea or pneumonia also requires its own appropriate treatment.

In the treated group of 39 dogs, 89.7% required hospital care. The median hospital stay was 5 days, ranging from 1–21 days. All 39 referral patients survived to discharge. The prognosis in severe HOD nevertheless remains guarded.

Activity and care of a recumbent puppy

Exercise is restricted during the painful phase according to veterinary instructions. A puppy lying in one position is turned to prevent pressure sores. Supportive care may also include gastrointestinal protection and individual nursing care. Treatment therefore involves more than observing a lame limb.

Recovery and follow-up

The outlook for mild or moderate HOD is generally good. A dog may start feeling better within 7–10 days of treatment beginning. This describes improvement in signs, rather than the length of a medication course. Signs may nevertheless recur until long-bone growth has finished. Some dogs have only a single episode.

Prevention

No reliably effective preventive measure suitable for every puppy can be named because the exact cause is unknown. A growing puppy is given balanced food appropriate to their age and size. Unnecessary supplements added to a complete diet are stopped according to the treatment plan. In feed labelling systems using these categories, a complete feed is intended to meet daily nutritional needs. A complementary feed supplements other food and is not the sole diet.

Some Weimaraner breeding guidelines recommend against breeding from a dog that has had HOD. Any possible vaccination association is assessed individually because a definite causal link has not been established. Vaccination history and previous suspected HOD form part of the overall veterinary assessment.

Check which life stage a food label specifies because puppies and adults have their own foods.

Important for dog owners

Observations help monitor treatment

Record how your puppy gets up, walks, eats and joins in normal activities. Also note visible swelling and tenderness when a limb is handled. Tell your vet about all foods and supplements because the diet is reviewed as part of treatment. The aim is to distinguish treatment response, a new episode and other problems requiring care.

Follow exercise restriction even when your dog starts to seem brighter. Position changes for a puppy remaining recumbent help prevent pressure sores. Have new pain or deteriorating movement reassessed because a similar sign can also arise from another disease. Agree at follow-up when normal exercise can increase and how limb growth will be monitored.

Frequently asked questions

Is HOD the same as ordinary growing pains or panosteitis?

HOD is a distinct disease of long-bone growth regions. It can involve bilateral swelling and high fever. Panosteitis instead involves medullary cavity changes and variable lameness. A lame puppy is therefore not classified at home from their growing age alone: a vet investigates the cause.

How young can a puppy develop hypertrophic osteodystrophy?

The usual onset is around 2–8 months of age. In a study of 39 referral dogs, ages ranged from 8–32 weeks. HOD has nevertheless also been described in small breeds and dogs as old as 15 months. Age and size guide suspicion, but investigations confirm the diagnosis.

Does a puppy recover completely from HOD?

The prognosis for mild or moderate disease is generally good. Signs may improve within 7–10 days of treatment starting. Some dogs nevertheless develop further episodes during growth. Severe growth plate damage can leave a permanent limb deformity, so recovery is also monitored in terms of skeletal growth.

Can HOD be treated with a vitamin supplement?

Vitamin C deficiency has not been confirmed as the cause of HOD. Treatment focuses on relieving pain and inflammation. The diet should be suitable for the puppy and balanced. Unnecessary supplements may be stopped under veterinary guidance, but reviewing food does not replace examination and treatment of a severely ill puppy.

Does every puppy with HOD need CT?

No. Ordinary X-rays are the first imaging investigation for HOD. CT can help particularly with vague signs or very subtle bone changes. Alongside images, your vet considers age, signs and clinical examination findings. Testing is selected according to what investigating the problem requires.