Case 180720 -3

10-year-old, female, spayed, Beagle mix-breed dog.

This patient presented to the UC Davis Neurology Service for acutely being down at home. She was noted by the owners to be dribbling urine and then suddenly went splay legged and was unable to stand.

On presentation and physical examination, she was paraparetic with minimal voluntary movement. She had a short gait with absent conscious proprioception in the pelvic limbs. There was no elicited pain upon spinal palpation with intact panniculus reflex. Neuroanatomic localization was determined as T3-L6 myelopathy and imaging identified a T4 compression fracture of the fourth thoracic vertebra. Due to poor prognosis for full recovery euthanasia was elected followed by necropsy.

There is a compression fracture of the vertebral body of T4 and the spinal processes of T3 and T4 are freely movable at their base (transverse fractures). The spinal cord at this affected region is grossly compressed.

This slide has a longitudinal section of a vertebra with a thin sliver of an adjacent vertebra including the intervertebral disc. There is a generalized and marked decrease in medullary trabeculae (osteoporosis) with the remaining trabeculae being thin and often disconnected from other spicules of trabecular bone. There is increased scalloping of the trabecular margins with occasional osteoclasts within Howship’s lacunae and decreased numbers of lining osteoblasts. Similarly, vertebral endplates and cortices are thinned. Nearly mid-way through the smaller strip of adjacent vertebra, there is a focal compression/shear fracture, which disrupts the adjacent intervertebral disc resulting in extrusion of nucleus pulposus into the fracture site. The affected disc material has chondroid degeneration with disorganized chondrones and empty lacunae. Similarly, the fractured epiphyseal bone is variably necrotic with empty lacunae and trabecular bone pallor.

No special stains.

Vertebra (T4): osteoporosis with a compression folding fracture and adjacent nucleus pulposus rupture

The acute paraparesis and other neurologic deficits are attributed to the T4 vertebral pathologic (compression) fracture. The fracture is considered pathologic based on the associated osteoporosis identified in the examined sections. Osteoporosis is considered a relatively common form of metabolic bone disease, however, the discussion noted that this is likely underdiagnosed if not looked for or if cause of morbidity or mortality is not related to bone disease. It can also be challenging to identify if the changes are subtle and there is not a matched control specimen for comparison. While osteoporosis is considered a normal part of the aging process in the literature, there are additional physiologic situations and diseases that may accelerate, contribute to or cause an imbalance in bone resorption and bone formation. Examples are primarily nutritional such as deficiencies in calcium, phosphorous or copper, starvation, severe gastrointestinal parasitism, and inflammatory bowel disease with malabsorption syndrome. Other possible causes are corticosteroid-induced and disuse. Postmenopausal women are at higher risk.

The precise cause of the osteoporosis in this dog was not determined, but the animal did have a pituitary carcinoma, possibly secreting increased ACTH, leading to hypercortisolism, a known risk factor for osteoporosis. The dog had polyuria and polydipsia and the adrenal glands were determined to be enlarged by ultrasound; findings supporting potential hyperadrenocorticism.

Linden E. Craig, Keren E. Dittmer, Keith G. Thompson. Bones and Joints. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol. 1, 6th ed. Philadelphia, PA: Elsevier; 2016:63–67.