Page 246 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Musculoskeletal system: 1.5 The hindlimb 221

VetBooks.ir Aetiology/pathophysiology 1.414
The pathophysiology of this condition is not clearly
understood, but theories include humoral, neural
and hypoxic mechanisms. Hypertrophic osteopathy
has been associated with thoracic pathology such as
lung abscessation, tuberculosis, neoplasia, pulmo-
nary infarction and rib fractures, but it has also been
diagnosed in animals with abdominal metastases,
and in one report it was twice related to pregnancy.

Clinical presentation
Horses are commonly presented for investigation of
the enlarged bones, but signs related to the primary
lesion such as cough, nasal discharge or chronic
weight loss may precede and be the reason for
investigation. The clinical presentation is variable,
but commonly the condition involves progressive
deterioration over a prolonged period of time. The
distal limbs may be symmetrically or asymmetri-
cally swollen and warm, and there may be some
restriction and pain on palpation and manipulation.
Affected animals may have a stiff gait and commonly
are reluctant to move.

Differential diagnosis Fig. 1.414 Dorsopalmar radiograph of a horse
Fluorosis; nutritional secondary hyperthyroidism; with hypertrophic osteopathy. Note the new bone
and for the primary underlying disease, intratho- formation at the level of the third metacarpal bone
racic or intra-abdominal mass (neoplasia, abscess). and proximal phalanx.

Diagnosis Management
Diagnosis is based on clinical signs and radiographic The primary condition should be treated if pos-
findings. Radiography commonly reveals a palisade sible, and the bone lesions may subside following
pattern of periosteal new bone formation parallel to resolution of the primary problem. If no underlying
the cortices of the long bones (Fig. 1.414). Although disease is identified, symptomatic treatment, mainly
the new bone may be close to the joint margins, the with NSAIDs, is worthy of consideration. In a small
articular surfaces are rarely involved. Bone scintigra- proportion of horses the condition may resolve
phy may show an increased uptake in the distal limb, either spontaneously or following treatment of the
even before radiographic changes. Haematology and primary cause.
biochemistry may reveal abnormalities related to the
underlying cause. Efforts should be made to identify Prognosis
the primary condition. This should include upper If the primary lesion is not identified or treated,
airway endoscopy, bronchoalveolar lavage, thoracic the prognosis is poor and, because of the debilitat-
radiography and ultrasonography, rectal palpation, ing nature of the condition, euthanasia is commonly
abdominal centesis and ultrasonography. More inva- necessary. Where the primary condition can be
sive diagnostic procedures may include lung biopsy, identified and treated, the prognosis is better but still
pleuroscopy and laparoscopy. guarded.