Idiopathic hypertrophic osteopathy in a cat

Hypertrophic osteopathy in South Australian koalas (Phascolarctos cinereus) with concurrent pulmonary actinomycosis

Pulmonary actinomycosis is described in 17 South Australian koalas necropsied between 2016 and 2019. From these cases, four koalas had secondary hypertrophic osteopathy. Plain radiographical and computed tomography images demonstrated periosteal reaction on multiple appendicular skeletal bones in all cases, including scapula, humerus, ulna, radius, ilium, femur, tibia, fibula, metacarpus, metatarsus and phalanx. Grossly, periosteal surfaces of the metaphyses and diaphyses of long bones were thickened and roughened; microscopically, this was characterised by bi-layered proliferation of well-differentiated trabecular bony spicules oriented perpendicular to the cortex (pseudocortices) and separated by vascular connective tissue, typical for hypertrophic osteopathy. Well characterised in domestic species and rarely reported in marsupials, this is the first radiographical and pathological characterisation of hypertrophic osteopathy in koalas, associated with pulmonary actinomycosis in all cases.

Renal adenocarcinoma associated with hypertrophic osteopathy in a cat

Case summary

A 10-year-old neutered male domestic shorthair cat was diagnosed with renal adenocarcinoma associated with hypertrophic osteopathy. The cat was referred for chronic ambulation difficulties. The physical examination showed a painful thickening of all four limbs, a right cranial abdominal mass and a conjunctival hyperaemia. Radiographic findings were consistent with extensive periosteal new bone formation involving not only the diaphyses of the fore- and hindlimbs, but also of the pelvis, tarsus and carpus. Abdominal ultrasonography and CT revealed a mass within the right kidney and a primary neoplasm was suspected. A ureteronephrectomy of the right kidney was performed and histopathology confirmed the diagnosis of renal adenocarcinoma. Although clinical improvement of the lameness occurred after surgery, no radiographic changes of hypertrophic osteopathy lesions were observed at the 9-month follow-up.

Relevance and novel information

Feline cases of hypertrophic osteopathy are rarely reported in the literature and only a few of them were associated with abdominal neoplastic diseases. To our knowledge, this is the first case of renal adenocarcinoma associated with hypertrophic osteopathy in a cat.

Hypertrophic osteopathy in a cat with cardiac interventricular septal defect

A 3-year-old mixed-breed female cat was diagnosed with a ventricular septal defect of the heart through an echocardiogram. After a 9-month treatment, progressive and diffuse hard thickening of all limbs was observed, which on radiographic examinations, revealed a marked thickening of the long bones. The necropsy findings were limited to the appendicular skeleton and thoracic vertebrae, in addition to a severe cardiac interventricular septal defect and lung edema. The histological evaluation revealed severe replacement of the cortical bone by spongy bone in all bone fragments examined. This is the first report of hypertrophic osteopathy occurring in association with a cardiac malformation in a cat.

Hypertrophic osteopathy in a cat with a concurrent injection-site sarcoma

Case summary An 11-year old neutered female domestic shorthair cat presented for investigation of a large, partially ulcerated skin mass in the area of the left scapula. The cat had been vaccinated 6 weeks previously in the same area. Haematology showed a marked neutrophilia and monocytosis. Tru-cut biopsies were taken and histopathology was consistent with a high-grade soft tissue sarcoma. Thoracic radiographs and abdominal ultrasound revealed no abnormalities. Moderate mixed (palisading, brush border and smooth) periosteal reaction was seen on the diaphysis of long bones at the time of the radiographic examination. Magnetic resonance imaging of the mass showed infiltration within deeper tissues and the owners elected euthanasia. Post-mortem examination confirmed the presence of hypertrophic osteopathy with a concurrent injection-site sarcoma. No evidence of intra-thoracic or intra-abdominal disease was found.

Relevance and novel information To our knowledge, this is the first report where hypertrophic osteopathy has been described in a cat with a soft tissue sarcoma, most likely an injection-site sarcoma.

Polyostotic hyperostosis in a domestic shorthair cat

CLINICAL PRESENTATION

An 11-year-old male neutered domestic shorthair cat was presented for investigation of weight loss and inappetence. On physical examination there was palpable enlargement and thickening of many bones, and this finding was confirmed radiographically. PROPOSED DIAGNOSIS: Based on clinical, radiological and histopathological findings, a polyostotic bone disease, best described as generalised idiopathic hyperostosis, was diagnosed. This condition has not been reported in cats previously. Canine and human diseases with similarities to this presentation are discussed.

Musculoskeletal oddities in the cat: an overview of some curious causes of lameness

PRACTICAL RELEVANCE

Cats, both young and old, can suffer a variety of weird and wonderful musculoskeletal conditions that are a cause of lameness. These include developmental, metabolic and nutritional bone diseases, ectopic mineralisation disorders, conditions that cause lameness or exercise intolerance and primarily or secondarily affect muscle, and lastly pad conditions.

CLINICAL CHALLENGES

These conditions are mostly rare and can be challenging to diagnose. The aim of this review is to bring these conditions to the attention of practitioners so that, if they are encountered, further research around the topic can be undertaken. Radiographic changes and diagnostic tests that can be used to try to confirm diagnoses are described.

EVIDENCE BASE

These unusual causes of lameness are the subject of multiple single case reports or small case series, many of which are relatively old. The evidence presented here is drawn from these articles. However, it is not possible within the scope of this review to discuss all the conditions in as much detail as they may warrant, or to make reference to every article relating to them.

Hypertrophic osteopathy associated with a renal adenoma in a cat

Hypertrophic osteopathy is a hyperostotic syndrome of the appendicular skeleton that is most commonly associated with intrathoracic neoplasia or inflammation. The condition is rarely associated with intra-abdominal lesions. The majority of cases have occurred in dogs and human beings, with fewer cases reported in cats, horses, and other species. A 15-year-old male neutered Domestic Shorthair cat presented for swollen limbs and difficulty in ambulation. Radiographs and gross postmortem revealed severe periosteal hyperostosis of the diaphysis and metaphysis of all 4 limbs, including the humerus, radius, ulna, carpi, metacarpi, femur, tibia, tarsi, metatarsi, and phalanges. The axial skeleton was spared. Hyperostotic lesions were characterized microscopically by lamellar bony trabeculae separated by adipocytes and scant hematopoietic tissue. In several areas, fibrovascular connective tissue, woven bone, and islands of cartilage were also present. A 2.5 cm × 2.5 cm perirenal neoplasm compressed the left kidney and adrenal gland. This mass consisted of well-differentiated tubules of cuboidal epithelial cells and was most consistent with a renal tubular adenoma, because mitotic figures were rare, and no distant metastases were found. Thoracic pathology was absent. Hyperostosis was consistent with hypertrophic osteopathy secondary to the renal adenoma. The pathogenesis of hypertrophic osteopathy is uncertain, but predominant theories point to increased peripheral circulation and angiogenesis as a key initiating event. Recent literature highlights the potential role of vascular endothelial growth factor and platelet-derived growth factor in the human condition. The mechanism by which this renal adenoma caused hypertrophic osteopathy is unknown.