Having come from the other side of the country, our vet school curriculum gave Potomac Horse Fever a fleeting glance of attention. The first case of the season presented last week, and throughout the work-up, I had that feeling of curiosity like when when you visit a place for the first time that you’ve only seen on TV or read about. It the combination of having knowledge and actually applying it in clinical context…academia meets practice. It was an exciting change from the ‘usual’ cases…the typical medicine caseload has resembled a constant trickle of RAO, gastric ulceration and corneal ulcers.
the 1st PHF Case
My first PHF patient was a 12 year old QH mare that presented to the hospital with a 3 day history of mild colic, lethargy, fever, increasing soft manure and bilateral front limb soreness. The referring veterinarian had run a CBC that revealed a mild leukopenia of 4,600 cells. The mare had all the red flags (leukopenia, fever, diarrhea) that necessitate adherence to a stricter level of bio-security protocols and restrictions. We bypassed the hospital and went straight for the isolation ward.
On arrival, she was in good body condition and ambulated well, although bilateral front end lameness was apparent (Grade 2/5). Abnormalities found during her initial physical examination included clinical dehydration of 8% and digital pulses increased in the front when compared to the hind (although not bounding). Her vitals were normal, although she had received Flunixin within the last 3 hours. Aside from a mild leukopenia of 4,500 cells, the rest of her work-up included normal rectal palpation, normal ultrasound findings and no other clinic pathology abnormalities.
She was started on a bolus of plasmalyte (10 liters), followed by 1.5x maintenance fluid rate (1.5 liters/hour). She was also started on oxytetracycline at 10 mg/kg as the robust initial 3 day dose. This was given in 1 liter NaCl over the course of an hour. She remained comfortable overnight, maintained a normal appetite and normal manure production.
The next morning, I palpated bounding digital pulses bilaterally on her front feet. Hoof heat was increased and with the next few hours she began shifting her weight and was very reluctant to navigate around the stall. At this point, she was started on cryotherapy (ice boots) and continued to receive the anti-endotoxic dose of Flunixin twice daily. DMSO and a butorphanol CRI were started. Even on the butorphanol CRI, she became more progressively painful with an horse Grimace score of 10/12.
Radiographs revealed no evidence of laminitis changes and we’re used to establish her baseline. It took over an hour to get radiographs of all four feet because of her extreme pain and reluctance to bare weight. Without her willing to stand on blocks to radiographs the distal phalanx, we resorted to piling up shavings so that she was 4 inches elevate from the stall floor. She would absolutely not tolerate standing on any 3 limbs, so holding each foot for radiographs wasn’t an option. Hindsight being what it is, I will perform nerve blocks in the future to help facilitate the radiographs.
The mare spiked a couple 103 fevers in the first 48 hours after presentation, but afterwards remained afebrile. Although afebrile, the concern about impending laminitis led us to continue with the ice boots on all four feet at all times. I’ve used “ice-bracelets” in the past, but this hospital utilized two empty 5 liter plasma late bags and does a “double-bag” technique. The outer bag contains the ice and is finest rated to facilitate drainage while the inner bag is intimately against the foot and sealed to prevent the foot from endless soaking. Although the double-bag technique is used hospital-wide, there exists some controversy over the method of securing the bag. Some clinician’s prefer to use 2 inch white tape around the top of the bag (at the level of the distal metacarpal/metatarsal) while others insist on creating a purse-string with umbilical tape passing through holes (similar concept to tying shoes with shoelace holes and shoelaces).
Over the next couple days, the mare deteriorated systemically and repeat radiographs revealed sinking and rotation. Due to concerns about quality of life, the euthanasia was elected. The mare had recently come from the Midwest and was not vaccinated for PHF.
the PHF Dam
Within a couple hours have euthanizing my first patient, I heard the pager sounds echoing through the hospital in sequence. My pager eventually went off (it awkwardly goes off 45-60 seconds after everyone elses’).
ER PHF to arrive in 1 hour.
The second PHF case arrived in stable condition, with no foot soreness and having already been on Oxytetracycline for 3 days. As a precaution, the trainer wanted the horse medically managed in hospital. It was during the middle of this workup that we received another hospital alert
Adult horse with suspect PHF ETA 5PM.
And as if the dam holding back PHF had broken, we had 5 more PHF cases present to the hospital over the course of 3 days. Fevers of unknown origin, foot soreness with colicky signs…everything was starting to look like PHF. It also happened to be the summer storm-a-thon. Like a torrential downpour, or the monsoons in Arizona, we received a whiplash in the form of PHF. As the PHF novelty gradually wore off, the idea of a RAO work-up, gastroscopy appointment or corneal ulcer assessment gradually gain appeal.
For those interested, below is the abstract of a peer-reviewed article about the use of cryotherapy in an attempt to reduce clinical development and presentation of laminitis.
Prophylactic digital cryotherapy is associated with decreased incidence of laminitis in horses diagnosed with colitis
A. Kullmann1, S. J. Holcombe1,*, S. D. Hurcombe3, H. A. Roessner1, J. G. Hauptman2, R. J. Geor1 andJ. Belknap3. DOI: 10.1111/evj.12156
Summary: Recent research suggested that prophylactic digital cryotherapy (ICE) improved lameness scores, diminished histological changes and early laminar inflammatory signalling in horses following oligofructose administration. In clinical practice, horses at risk for sepsis-associated laminitis receive ICE. Evidence to support this practice is lacking.
Methods: Medical records for horses admitted to 2 university hospitals diagnosed with colitis with evidence of systemic inflammatory response from 2002 to 2012 were reviewed. Horses were excluded if they exhibited signs of laminitis at admission, were ponies, miniature or draught breeds, or <2 years old. Data were analysed using univariate and multivariate logistic regression.
Results: Twenty-seven of 130 horses (21%) developed laminitis. Seven of 69 (10%) horses treated with ICE developed laminitis compared with 20/61 (33%) horses that developed laminitis but did not receive ICE. Factors associated with laminitis included site of hospitalisation, admission respiratory rate and blood L-lactate, and ICE, P<0.05. Horses treated with ICE had 10 times less odds of developing laminitis compared with horses treated without ICE (odds ratio 0.11, 95% confidence limit 0.03–0.44). Sixteen horses (16/130, 12%) were subjected to euthanasia in hospital. Fourteen of these horses had laminitis and 2 did not develop laminitis. Survival for horses with colitis that developed laminitis was 13/27 (48%) compared with survival for horses with colitis that did not develop laminitis, 101/103 (98%).
Conclusion: Laminitis occurred in more clinically compromised horses. Use of ICE reduced the incidence of clinical laminitis in the study population suggesting that digital cryotherapy is an effective prophylactic strategy for the prevention of laminitis in horses with colitis.
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