Ros Tate had never heard of the condition guttural pouch mycosis (GPM) until her dressage mare, Supreme’s Shania, was rushed to hospital last May.

After learning that emergency surgery was necessary, Ros endured a traumatic 24 hours before her mare sadly lost her life.

“My daughter had called me to say that Shania was having a nosebleed,” says Ros, who had bought the young Don Schufro daughter from Denmark two years previously. “I had never seen anything like it: blood was pouring from her nose and mouth. Luckily, one of our vets lives in our village. She recognised instantly that it was guttural pouch mycosis and told me to get Shania straight to hospital.”

Blood was pouring from Shania’s nose and mouth

The vets at Fyrnwy Equine Clinic waited for Shania’s condition to stabilise after the trauma of the bleed before they operated, but she collapsed on the way to theatre.

“This stopped her breathing, so she underwent an emergency tracheotomy,” explains Ros. “They couldn’t operate until the swelling had subsided, but the next morning she suffered another massive bleed and had to be put down.

“The shock of losing my beautiful mare in such horrific circumstances is something I’ll never forget.”

Artery erosion

The story serves to highlight the potential of GPM to kill. What can cause such a dramatic sequence of events? Phil Cramp MRCVS explains that the problem starts in two hard-to-access pockets located within the horse’s head.

“The guttural pouches are extensions of the Eustachian tube, an air-filled canal that connects the throat to the middle ear,” he says. “There are two pouches, one on each side, located just below the ear in the throatlatch region. Their purpose remains unknown.

Shania in hospital, recovering from the first bleed

Possible uses include pressure equalisation across the ear drum or warming of inhaled air, or they could serve as a resonating chamber for vocalisation or an aid in the cooling of blood that flows to the brain during exercise.

“Each pouch is divided into two compartments by the stylohyoid bone,” adds Phil. “There are a number of important structures within each pouch, including nerves that control swallowing, breathing and facial expression. Several major blood vessels also pass along the pouch walls, most importantly the internal and external carotid arteries and the maxillary artery.”

Phil explains that GPM is a fungal infection of one or both pouches.

“While the exact cause of the condition remains a mystery, the fungus Aspergillus spp. is often detected — alone, or in combination with other fungi,” he says. “Fungal plaques form within the pouches, most commonly along the walls of the major blood vessels and typically affecting the internal carotid artery.

“This fungal infection grows into and erodes through the vessel walls, resulting in the formation of an aneurysm [an excessive swelling]. This eventually leads to a hole in the vessel wall — and potentially a life-threatening haemorrhage.”

Red alert

According to Phil, there is nothing an owner can do to prevent GPM.

“It is vital to recognise the clinical signs and act promptly,” he says. “A nosebleed is the most common sign — this is typically moderate to severe and the blood is bright red in colour as it is coming direct from an artery.

“There are usually a number of smaller episodes before a potentially fatal bleed. While it’s sensible to contact your vet about any nosebleed, a significant loss of blood should be treated as an emergency.

“The second most common sign is difficulty eating and swallowing, a condition called dysphagia,” adds Phil “This occurs if the fungus damages the nerves that control tongue movement and swallowing. Dysphagic horses often struggle to eat and may be seen quidding [dropping unchewed feed], packing feed in their cheeks and coughing because they cannot swallow normally.

“Other signs less commonly observed include the development of Horner’s syndrome, which causes a drooping eyelid, constricted pupil, sunken eye and patchy sweating on one side of the neck only. There may be white nasal discharge, an abnormal head posture and pain in the throatlatch region, or an abnormal respiratory noise due to damage to the nerves that supply the muscles of the throat.

“These more generalised signs can be caused by many other disease processes, but if any were present, your vet would always look to rule out a guttural
pouch disease.”

Phil explains that a definitive diagnosis can be made by performing endoscopy of the guttural pouch, which involves passing a small, flexible tube with a camera tip or fibre optics up the horse’s nose.

“Once the endoscope has been passed into the nasopharynx, which is a cavity located above the soft palate, blood can typically be seen coming from one or both of the guttural pouch openings,” he says. “As the endoscope enters one of the pouches, it is usually possible to visualise the fungal plaque — seen as white, tan and black membranes overlying one or more blood vessels. This is 100% diagnostic.

“At this point, you should be either taking your horse into your vet’s clinic, an equine hospital or arranging referral to a specialist centre for treatment. Once there, the horse will undergo further evaluation in an attempt to determine exactly where the fungal plaque is growing and which vessel is affected.”

Worst-case scenario

While surgery is effective in the majority of cases (see box), Shania never reached the operating table.

“It’s pot luck how big the hole is in the carotid artery,” explains Jim Tipp MRCVS of Fyrnwy Equine Clinic. “The first bleed is usually a major warning and the second is likely to be fatal, so the situation is a ticking time bomb until surgery can take place. You really don’t know when the next bleed might occur — it could be an hour later, or a month.

“Unfortunately, Shania’s circumstances formed the worst-case scenario,” he says. “She had what’s called a dissecting haemorrhage, where she bled into the tissues around her brain. The severity of the fungal infection and the extent of the resulting bleed made surgery impossible.”

Reflecting on her mare’s history, Ros adds: “She did drop food from her mouth, from first arriving in the UK, and a day doesn’t go by when I don’t wish I had persisted in investigating this.

“The condition is treatable, if caught in time,” she adds. “If this story helps another owner recognise the signs, at least some good may come out of Shania’s death.”

Surgical options

Vet surgeon Phil Cramp explains that guttural pouch mycosis requires surgical treatment.

“There are reports of successful medical management consisting of treatment with topical and systemic anti-fungal drugs, but the risk of a fatal haemorrhage is too high,” he explains. “Surgery is aimed at occluding [closing up] the affected artery. Without blood supply, the fungal growth stops and can then resolve without further treatment. Most surgeons elect to treat the fungus topically for a week or so after surgery, however, to ensure a successful resolution.

“There are two main surgical procedures, both of which require a general anaesthetic. One involves placing an inflatable balloon, attached to a flexible catheter, into the affected artery via an incision in the upper neck. Once positioned, the balloon is inflated to stop the flow of blood.

“In another procedure, small coils or plugs are placed in the affected artery using a real-time imaging method called fluoroscopy. While very accurate, this technique requires specialist equipment and is not widely available.

“Success rates for both procedures are good, although it can take a long time for some of the clinical signs associated with nerve damage to disappear. The fungal plaques may take up to six months to resolve fully.”

Ref: Horse & Hound; 1 March 2018