Hypertrophic Osteodistrophy

Hypertrophic osteodystrophy (HOD), sometimes referred to as metaphyseal osteopathy, is an uncommon developmental orthopedic disease that affects rapidly growing large- and giant-breed dogs between 2 and 8 months of age. Although there is no known sex predilection, male dogs seem to be overrepresented.
According to case reports in the veterinary literature, breeds found to have a higher incidence of HOD include German Shepherds, Irish Setters, Weimeraners, Boxers and Great Danes.
Even though HOD occurs most often in fast-growing large and giant breed dog, it can also affect medium breed dogs like the Australian Shepherd, Labrador retriever, Australian Kelpie and Chesapeake Bay Retrievers.

Clinical signs:
Clinical signs vary from mild to severe. Dogs with HOD usually present with lameness in one or more limbs in association with signs that include swollen, warm and painful limbs, specifically at the metaphyseal regions of long bones. most affected bones are the radius, ulna and tibia. If multiple limbs are affected, the patient might be reluctant to stand up.
In severe cases, the patient may present systemic signs that include fever, lake of appetite, gastrointestinal symptoms, abnormal respiratory sounds and lethargy.

Etiology:
The etiology of HOD is currently unknown and is likely to have multifactorial causes. Several etiologies have been theorized in the literature including canine distemper virus (CDV), previous vaccination, hereditary causes, auto-immune disorders, increases vitamin and mineral uptake (excessive calcium supplementation is one proposed hypothesis) and over-feeding.

In Weimaraners, recent vaccination with a modified live vaccine has been proposed as a possible cause. The canine distemper vaccination has been a suspected causal factor due to the significant number of overlapping symptoms observed between systemically affected HOD puppies and dogs suffering from distemper. So far, no definitive linkage has been demonstrated.
However, because of familial clustering, HOD in the Weimaraner is suspected to have a genetic, or partly genetic, origin.

Diagnosis:
The clinician’s index of suspicion should be guided by signalment and clinical signs, in addition to thoroughly collecting patient history.
The diagnosis is confirmed with radiographs of the affected limbs. The presence of the “double physeal line”, consists of a radiolucent line that is parallel to the physis, is pathognomonic for HOD.  Histopathologic evaluation of an HOD affected bone reveals that the metaphyseal trabeculae is disrupted parallel to the growth plate, suggesting a disturbance in the endochondral ossification presumably secondary to a decreased blood flow to the metaphysis.

Treatment:
Treatment is depending on the degree of lameness and severity of symptoms, but generally consists of anti-inflammatory steroids, pain medications, gastrointestinal support, nutritional management and appropriate supportive care. Critically affected patients require hospitalization and more aggressive supportive care for prevention of life-threatening consequences.

Prognosis:
Prognosis is generally good in mild to moderate cases, while guarded in severely affected patients.
Relapses in adult dogs can be managed with NSAIDs or corticosteroids.
Unlike Panosteite, HOD can cause permanent damage to the growth plates and in some rare cases will determine permanent limb deformities.

Sources:

 J Selman, H Towle Millars, Hypertrophic osteodystrophy in dogs, J Small Anim Pract. 2022 Jan;63(1):3-9.

Abeles, V, Harrus, S, Angles, JM, Shalev, G, Aizenberg, I, Peres, Y and Aroch, I. (1999). "Hypertrophic osteodystrophy in six Weimaraner puppies associated with systemic signs". Vet Record. 145 (5): 130–134.

 Baumgartner, W., Boyce, RW, Aldinger, S, Axtheim, MK, Weisbrode, SE, Krakowka, S and Gaedke, K. (1995). "Metaphyseal bone lesions in young dogs with systemic distemper virus infection". Vet Microbiol. 44 (2–4): 201–209. 

Crumlish P, Sweeney T, Jones B, Angles J (2006). "Hypertrophic osteodystrophy in the Weimaraner dog: lack of association between DQA1 alleles of the canine MHC and hypertrophic osteodystrophy". Vet J. 171 (2): 308–13.

Nina R Kieves , Juvenile Disease Processes Affecting the Forelimb in Canines, Vet Clin North Am Small Anim Pract. 2021 Mar;51(2):365-382.

Jennifer Demko DVM, Ron McLaughlin DVM, DVSc, Developmental Orthopedic Disease, Vet Clin North Am Small Anim Pract. 2005 Sep;35(5):1111-35, v.