EQUINE VETERINARY EDUCATION / AE / FEBRUARY 2013 67 Clinical Commentary Septic osteitis and osteomyelitis in foals – are antimicrobials alone enough? C. Koch* and S. Witte Equine Clinic and Department of Clinical Veterinary Medicine, Vetsuisse-Faculty, University of Bern, Bern, Switzerland. *Corresponding author: email: [email protected] Keywords: horse; foal; septic osteitis; septic osteomyelitis; medical treatment; doxycycline Introduction fibrinogen concentrations and blood cultures, however, can The case report by Lawrence and Fraser (2013) describes the be helpful in diagnosing O/OM (Sayegh et al. 2001; Newquist successful management of 2 weanlings with septic osteitis of and Baxter 2009). the proximal sesamoid bones, using prolonged (6 weeks) Radiography is most commonly used to confirm and follow antimicrobial therapy alone. Doxycycline, an antimicrobial a septic bone lesion. Bone lysis may not be recognised with excellent bone penetration properties, was deemed radiographically until at least 4–5 days post infection, at a time essential to treatment success. In contrast to the poor when the bone has lost 30–50% or more of its mineral content outcome in previously reported cases of septic sesamoid bone (Turner 1987; Bramlage 1998; Goodrich and Nixon 2004). In osteitis, the authors were able to show the value of a cases with concurrent infarction, this time lag may be as great conservative approach over surgical debridement. The as 2–3 weeks (Wegener and Alavi 1991; Bertone 1999). question is to what extent are we able to extrapolate this to Delayed diagnosis and associated extensive lysis may result in the general treatment of septic osteitis and osteomyelitis in pathological fracture, with a negative impact on prognosis young horses? (Fig 1). Advanced imaging (magnetic resonance imaging [MRI] or computed tomography [CT]) may allow earlier recognition (Sayegh et al. 2001; Easley et al. 2011) and provide Etiopathological, clinical, and information on the extent of the lesion (Fig 2). While the diagnostic features severity of the radiographic lesion does not necessarily appear Septic osteitis (O; infection of bones lacking a medullary to affect long-term outcome (Steel et al. 1999; Kay et al. 2012), cavity) and osteomyelitis (OM) are common in foals up to age its location is more likely to determine future soundness. approximately 4 months and often involve adjacent synovial Successful elimination of infection manifests radiographically structures (Firth 1983; Neil et al. 2010). The source of bacteria, as sharp delineation of the original defect and surrounding their species and the physiological and anatomical sclerosis (Fig 3). This being said, it can take many months for a considerations that favour their growth at sites of predilection defect to regain mineral density, if at all (Lawrence and Fraser are summarised by Lawrence and Fraser (2013) and elsewhere 2013). Therefore, a positive clinical progression (decreased in the literature (Firth 1983; Brewer and Koterba 1990; Schneider swelling and lameness) and improved results of repeated et al. 1992; Vatistas et al. 1993; Hardy 2006; Neil et al. 2010). clinicopathological testing represent more important In mature horses, O/OM are usually associated with indicators of early success in treatment. penetrating injuries or previous surgical interventions. In the report by Lawrence and Fraser (2013), 2 weanlings, aged 5 and Current treatment strategies in man and equids 6 months, were affected by septic osteitis of the proximal In their ‘plea for general conservatism in the treatment of sesamoid bones (PSB). In horses of this age haematogenous septic osteomyelitis of the skull and face’ Blair and Brown seeding of bacteria remains the most likely initiating cause in (1927) remind human practitioners of an old Italian proverb the absence of external injury, although a primary septic focus that states ‘He who goes slowly goes safely; he who goes elsewhere in the body is rarely identified (Wisner et al. 1991; safely goes surely’. Unfortunately the question as to just Dabareiner et al. 2001; Witte and Rodgerson 2005; Sherman how ‘safe’ or ‘sure’ a conservative approach is, remains et al. 2006). It is assumed that the relatively convoluted blood unanswered in both human and equine medicine. supply to the axial borders of the PSB and the intersesamoidean Current treatment recommendations in the equine ligament makes them predilection sites for haematogenous veterinary literature include surgical debridement of bone as septic osteitis and desmitis in weanlings and mature equids a primary course of action to address O/OM (Goodrich and (Wisner et al. 1991; Dabareiner et al. 2001; Barr et al. 2005; Nixon 2004; Schneider 2006; McIlwraith 2007). In contrast, Sherman et al. 2006; Lawrence and Fraser 2013). treatment of the human equivalent (acute haematogenous Lameness, focal pain and swelling (oedema and effusion) osteomyelitis [AHO] in paediatric patients) appears to focus dominate the clinical picture of O/OM (Bramlage 1998). In on prolonged systemic antimicrobial therapy (Le Saux et al. cases with effusion, synovial fluid analysis as well as culture and 2002; Peltola et al. 2010). A recent prospective, randomised sensitivity testing provide valuable information (Bramlage 1998; trial investigating appropriate antimicrobial treatment Sayegh et al. 2001). With the exception of an elevated body regimens found that extensive surgical interventions are rarely temperature, there is often a paucity of signs indicating a necessary in children (Peltola et al. 2010). The exception to systemic response (Goodrich and Nixon 2004). Plasma this is the presence of an obvious abscess, from which © 2012 EVJ Ltd 68 EQUINE VETERINARY EDUCATION / AE / FEBRUARY 2013 Fig 1: Dorsolateral-palmaromedial oblique radiograph of the right front fetlock and corresponding trans-sectional CT image at the indicated level (dotted line) of an 11-month-old Welsh Pony. The pony presented with a nonweightbearing lameness of this limb of 3 weeks’ duration. Effusion of both the digital sheath and metacarpophlangeal joint was present. The medial PSB had a large septic bone lesion, identified with conventional radiographs (arrowheads). Proximal to this, a pathological fracture of the medial PSB had occurred (arrow) as seen on CT imaging. Fig 2: Dorsopalmar radiograph of a right front fetlock and corresponding MR image at the indicated level (dotted line) of a 12-year-old Camargue Pony presented with chronic, intermittent moderate right forelimb lameness. Lameness was abolished with intrathecal anaesthesia of the digital sheath, after which the horse showed a mild left forelimb lameness. Chronic, aseptic lytic lesions affecting the axial border of the medial PSB (arrowheads and white arrow) were present in both front limbs. purulent material is aspirated (Blyth et al. 2001; De Boeck to have inoperable lesions due to extensive physeal 2005; Goergens et al. 2005). The continued emergence of involvement or surgically inaccessible locations such as the multiresistant pathogens such as community-acquired ilium or navicular bone. A conservative approach was methicillin-resistant Staphylococcus aureus in human patients therefore elected due to the morbidity likely to result from has resulted in an increased necessity for surgical intervention surgical intervention. Rather surprisingly, therefore, 7 of these 9 (Darville and Jacobs 2004; Harik and Smeltzer 2010). Surgical foals (78%), compared with 80 of the remaining 98 foals (82%) exploration and debridement are also indicated if a patient were reported to have a successful outcome (one foal was does not respond to empiric antibiotic therapy within an subjected to euthanasia without pursuing treatment). appropriate time frame by showing persisting signs of pain Another recent report focused on the treatment of septic and fever (Stanitski 2004; Goergens et al. 2005; Harik and osteomyelitis of the patella (Kay et al. 2012). There, 6 of 8 foals Smeltzer 2010). (75%) made a full recovery. Notably, all surviving foals were Closer analysis of the data presented in reports of O/OM treated without surgical debridement of the patellar lesion, but cases in the veterinary literature (Witte and Rodgerson 2005; all received intralesional antimicrobials. Although numbers are Neil et al. 2010; Kay et al. 2012; Lawrence and Fraser 2013) small, these reports suggest that cases treated without bone allows us to consider the value of an initial conservative debridement can have an equally successful outcome when approach in the equine case with lytic bone lesions. In a compared to previous studies (Schneider et al. 1992; Vatistas retrospective study of 108 foals, medical therapy alone et al. 1993; Axon et al. 1999). Figures 3–5 are further examples was pursued in 9 (Neil et al. 2010), which were considered of cases treated successfully with antimicrobial therapy alone. © 2012 EVJ Ltd EQUINE VETERINARY EDUCATION / AE / FEBRUARY 2013 69 a) b) Fig 3: Initial (a) and one month follow-up (b) lateromedial radiographic projections of the left stifle of a 4-week-old Thoroughbred foal affected with O/OM of the distal femoral physis. Note the location of the patella (due to severe femoropatellar joint effusion) and extensive lytic lesions (arrows) upon initial presentation and the sclerotic demarcation (arrowheads) after successful treatment without surgical debridement. a) b) Fig 4: Caudocranial radiographic projections of the left stifle of a one-month-old Warmblood colt presented for an