Oxygen therapy helped treat guttural pouch mycosis in horses

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The endoscopic evaluation of the right guttural pouch of one of the horses in the study.
The endoscopic evaluation of the right guttural pouch of one of the horses in the study. Image A shows the horses at admission, with inflammatory lesions located on the stylohyoid bone (star) and the roof the medial compartment with regard to the internal carotid artery (arrow). Image B shows the results after nine days of topical oxygen therapy and a transarterial coil embolization procedure. The size of the lesions is reduced. The spiraled tip of the GP catheter is shown in position. Image: Lepage et al. https://doi.org/10.3390/ani11113329

Oxygen therapy shows promise as a treatment for fungal infections in the guttural pouch of horses, researchers report.

The condition, known as guttural pouch mycosis, is a rare but sometimes life-threatening disease. Signs include nasal discharge, neurological disorders, and nosebleeds.

The size, location, and appearance of the inflammatory lesions associated with the problem are variable and not necessarily related to the severity of the clinical signs.

Fungal cultures often highlight Aspergilli, a common fungus considered to be involved in the development of the problem.

The invasive Aspergilli damage tissue, including arterial walls and nerves in the area. Management of bleeding can be achieved with transarterial coil embolization, but if neurological disorders are present, they resolve only in roughly half of patients.

This poor outcome explains why there is a need to use additional treatments, such as topical antifungal therapy, or a way of modifying the guttural pouch environment by performing a salpingopharyngostomy − directly opening the guttural pouch to the larynx.

Olivier Lepage and his fellow researchers in France set out to test the feasibility and safety of topical oxygen therapy to reduce the fungal infection.

Even though Aspergillus species are highly aerobic and found in almost all oxygen environments, they are also capable of growth in low oxygen levels. Paradoxically, increased oxygen levels at the site of infection reduce fungal biofilm proliferation and the harmful effect of Aspergillus.

The researchers described a two-phase study designed to test the effects of topical oxygen therapy.  Oxygen from a cylinder was delivered via a tube with a spiral end, which had a series of holes. The tube’s successful placement in the guttural pouch − a horse has two, one on each side − was done under endoscopic guidance.

In a small pilot study, the authors found that the oxygen therapy was easy to perform in a standing horse, with no adverse effects. After more than two oxygen administrations, visible lesions decreased more quickly in the treated guttural pouches of eight horses than those left untreated.

Based on the results of the pilot study, a protocol was established for clinical cases presented at the hospital at the National Veterinary School of Lyon.

In this phase − the clinical study − topical oxygen therapy was administered for 45 to 60 minutes at 15 litres per minute in six horses with guttural pouch mycosis.

One horse received only the oxygen therapy, while the other five were also given a transarterial coil embolization.

The authors said clinical signs at admission varied between horses, which made comparison difficult.

However, after oxygen therapy and discharge from hospital, nasal discharge resolved in three horses, and improvement was noted in a fourth.

Between days 2 and 10 after admission, endoscopic examination indicated size reduction and alteration in the appearance of all the visible inflammatory lesions.

The partial or total recovery of neurological disorders was seen in about half of the affected horses.

The horse who did not require a transarterial coil embolization to stem bleeding provided important observations confirming the effectiveness of oxygen therapy, the researchers said.

Oxygen therapy was immediately given to this animal, and, within 48 hours of admission, the size reduction and change in the appearance of the lesions definitely ruled out the need for arterial occlusion.

“In this particular situation, we either witnessed a spontaneous regression, which is unlikely, or observed a mechanism that reversed the course of the condition with progressive and complete resolution of the lesions consequently.”

On the basis of the study and the authors’ experience with more recent cases, it may be recommended to institute oxygen therapy in one or both guttural pouches as soon as the diagnosis is made and to continue this treatment for about 10 days.

“This clinical approach seems to reverse the course of the disease probably by affecting the development of fungi and increasing the effectiveness of the body’s natural defenses.”

In cases where both pouches are affected, oxygen can be delivered to both simultaneously through the placement of two different catheters.

Based on the findings, oxygen therapy can be recommended in two different clinical presentations, they said. If no history of nose bleeds exists, and if lesions are not overlying major arteries, oxygen therapy alone can be employed. In this case, an endoscopic examination is essential to assess the regression of the lesions moving away from vessels.

In horses at risk of nose bleeds, a multimodal approach with a transarterial coil embolization procedure should be performed.

“In both situations, topical oxygen therapy administration four times per day at 15 litres per minute for one to two weeks is probably sufficient to reverse the course of the underlying disease.”

The researchers said topical oxygen therapy alone or in combination with transarterial coil embolization is feasible and safe, with a propensity to reverse the course and the progression of inflammatory lesions without additional local or systemic treatment.

The study team comprised Lepage, Paola Di Francesco, Nicolas Moulin, Monika Gangl and Jean-Luc Cadoré, all with the National Veterinary School of Lyon, which is part of the University of Lyon; and Gaëtan Texier and Joffrey Marchi, with the French Armed Forces Center for Epidemiology and Public Health in Marseille.

Lepage, O.M.; Di Francesco, P.; Moulin, N.; Gangl, M.; Texier, G.; Marchi, J.; Cadoré, J.-L. The Effect of Topical Oxygen Therapy in Horses Affected with Mycosis of the Guttural Pouch: An Experimental Pilot Study and a Case Series. Animals 2021, 11, 3329. https://doi.org/10.3390/ani11113329

The study, published under a Creative Commons License, can be read here

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