Case history

An equine, female, American Trotter, 115 days old, was referred to the veterinary hos- pital presenting incoordination since the day before, that started with the forelimbs and extended to the hindlimbs. The owner denies previous infection by Herpesvirus or Lepto- spirosis in the property. The filly was treated previously with three liters of Ringer-lac-  tate solution, corticosteroids, flunixin me- glumine, trimethoprim-sulfamethoxazole, and 100mL of dimethyl sulfoxide (DMSO). Additional information regarding doses and treatment duration were not obtained. After therapy, the filly showed improvement  on the incoordination of the forelimbs. Howev- er, still had trouble getting up and nursing.

Clinical presentations

Physical exam showed a heart rate of 60 beats per minute (bpm), respiratory  rate  of 30 breaths per minute (bpm), congested mu- cous membranes, capillary refill time of two seconds.  There  were  no  adventitious   lung

sounds. At palpation, the cervical region had an increase in volume with fluctuant consis- tency on the atlantoaxial joint. The animal could not maintain itself stable when  up,  nor lifting its head. The hooves had elevat- ed temperature and distal a strong pulse was felt on the palmar and plantar arteries, being more intensive on the right forelimb.

Diagnostic testing

In the simple radiographic examination  of the vertebral column (Fig. 1), the initial sus- picion was a fracture of the odontoid process causing compression of the spine. After exam- ining the alterations in the radiographs associ- ated with clinical manifestations of the foal and the owner’s interests, euthanize was  chosen.

In order to get a more precise diagnosis, by educational and scientific interests, a myelog- raphy and myelotomography post-mortem was made. The first showed dorsal displace- ment of the spine on the atlantoaxial joint and in  the  dorsoventral  projection  a  thinning of

Figure 1. Cervical spine simple radiographic exam: Simple radiographic exam in laterolateral projection of the cranial cervical spine. The atlantoaxial relation is preserved, with an increase of volume in an area that has soft tissue radiopacity curved dorsal and ventrally (arrows), and a discrete diffuse heterogeneous radiopacity at the extension of the odontoid pro- cess ossification nucleus and of the axis cranial epiphysis extremity (*).

contrast columns and right lateral displace- ment, compatible with extradural compres- sion. Figure 2 shows which changes were de- tected in myelography, suggesting  infection.

The skull and the spine were sent to pa- thology for a more definitive diagnosis. After cutting the atlantoaxial joint, a high amount of purulent fluid was drained and a nodular formation of approximately two centimeters in diameter was observed in the joint, reach- ing the vertebral canal, with irregular and yellow surfaces, friable to the cut. No mac- roscopic changes were observed on the spine and the encephalon.

Marked  Wallerian  degeneration  was  ob-

served at the histopathology exam, especial- ly on the ventral area, with moderate axonal swollen focuses. The neural bodies present- ed strongly eosinophilic, reduced in  size, and with pyknotic nucleus (neuronal necro- sis). Both dorsal and ventral roots showed marked Wallerian degeneration. The brain showed moderate multifocal neuronal necro- sis, neurophagia focuses, and marked gliosis. Cytologic exam revealed a high amount of integrated and degenerated neutrophils asso- ciated to a high number of coccoid bacteria, and eventually, of intra and extracellular ba- cillus, suggesting a septic acute  inflammato-

ry process.

Figure 2. Cervical spine myelotomography: (A) Reformatting of the cervical spine in sagittal plane shows thinning and dorsal displacement of the ventral contrast column (white arrow) and presence of hypodense material in ventral vertebral canal in atlantoaxial transition (*). The dashed black line indicates the location of the transversal cut showed on the right. (B) Myelotomography in transversal plane, soft tissue window, shows a marked osteolysis on the right side of the axis’ cranial epiphysis (white arrow) and bone irregularity (black arrow). Hypodense homogeneous material in ventral vertebral canal on the right (*) compresses and displaces dorsolateral the spine to the left (extradural compression). A hypodense halo in soft tissues surrounds all the extension of this region (edema/inflammation) (white triangles).

A culture of the material collected  from the atlantoaxial region was made and no bac- terial growth was observed. Therefore, it was not possible to conclude with agent was the one responsible for the osteomyelitis occur- rence. The liquor was also evaluated, and no significant alterations were  found.

Assessments

Supporting the two foals’ reports that showed vertebral osteomyelitis and septic ar- thritis caused by R. equi infection (Guiguère & Lavoi,1994), the equine from this report probably had a hematogenous microorgan- ism spread, since the patient history did not show any information regarding trauma or medications administered by contaminated needles or tools that might have caused a lo- cal infection. However, the filly did not show signs of pulmonary or gastrointestinal disor- ders related to a possible R. equi or another pathogen infection.

Although the hematogenous spread through suppurative lesions originated by lungs seems common, most agents are successfully elim- inated from the blood by the endoplasmatic reticulum system, constituted by reticular and endothelial cells which  have  a  phagocyto-  sis function, performing the defense against pathogens (Prescott,1994; Cabtree & Jor- gense, 2012).

The low potential to eliminate the microor- ganisms by alveolar macrophages, when com- pared to macrophages of other parts of the or- ganism, suggests that R. equi causes vertebral infection through alveolar macrophage migra- tion. In this context, some studies report that the disease may occur spontaneously when there is no pulmonary injury or another kind of infection (Prescott, 1994), as happened to the filly in this report.

For  diagnosis  purposes,  radiographic eval-

uation is very important in the vertebral os- teomyelitis cases, but the classic radiographic lesions of osteolysis and bone proliferation may not be evident two to eight weeks after clinical signs appears, and bone lysis is not ra- diographic recognized until 30-50% of bone mineralization is lost. In a study made, four   to six foals presenting vertebral osteomyelitis did not showed radiographic changes, despite the extensive osteolysis observed at macro- scopic and histologic post-mortem evaluation (Stewart et al., 2007).

In conjunction with this information, in a published article regarding a 3-month-old colt that showed acute neurologic signs and was diagnosed with osteomyelitis of the occipital bone, the cervical radiographs and the ones made on the cranium basis were  inconclu- sive with no evidence of osteolysis or chang- es in the soft tissue radiopacity (Morresey et al., 2007). Along with the study mentioned, this report was also not able to detect typical changes that mark the  vertebral  osteomyeli- tis after the acute onset of clinical signs, only being able to find heterogeneous and diffuse radiopacity at the axis odontoid process and a likely loss of bone continuity, which led to a mistaken fracture  suspicion.

Another study about the computerized to- mography use in cases of cervical osteomy- elitis reports a 3-month-old foal with head tilt history after R. equi treatment that was sent to a CT exam that revealed a left parietal bone and occipital bone osteolysis, resulting in a caudal displacement of the latter. As a con- sequence of the infection that reached bone structures, a soft tissue mass was formed as- sociated to the osteolytic lesions, compressing the cerebellum and rostrally displacing the occipital lobe of the brain. The mass expand- ed medially, taking up part of the magnum foramen without invading the  atlantooccipital