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What is Pannus in Dogs?

Introduction

 

Pannus, commonly known as Überreiter's syndrome or chronic superficial keratitis (CSK), is a chronic progressive corneal disease that affects dogs. It is an autoimmune condition marked by immune cells invading the corneal epithelium and stromal layers. Other breeds may also be afflicted by this immune-mediated illness that affects the cornea, or clear part of the eye, but is most common in middle-aged German Shepherd dogs and Belgian Tervurens. While this condition is most common in dogs, it can also affect cats.


Pannus is a degenerative, commonly bilateral, and sometimes blinding disorder of the dog's eye. The outer layer or coat of the eyeball is made up of the cornea and sclera. This coat's primary function is to safeguard the internal ocular components. The cornea serves as a structural barrier and guards the eye against infections. It is a clear, avascular tissue. It gives the eye an appropriate anterior refractive surface along with the tear film. Two-thirds of the eye's refractive power comes from the cornea. Chronic inflammation of the corneal epithelium and anterior stroma in pannus results in neovascularization, pigmentation, and opacification.


What are the clinical signs of pannus?

 
The normal eye of a dog

First, a non-painful, elevated pink mass emerges on the cornea, usually on the lateral or outside side (if the eye is pictured as a clock face, the mass will frequently be discovered at the eight to eleven o'clock position on the pet's right eye or the one to four o'clock position on the left eye). Usually, both eyes are affected, but sometimes one seems worse than the other.

Early stages of pannus in a dog's eye
Early stages of pannus in a dog's eye

Commonly, the third eyelid seems enlarged and swollen. The lesion flattens, spreads out, gets pigmented or black in colour, and scarring covers more of the cornea as the pannus worsens. Chronic tissue alterations are characterized by advancing moderate-to-severe limbal melanocytic pigment invasion, fleshy granulation tissue infiltration into the anterior stroma, and moderate-to-severe corneal neovascularization. Additionally, a mucoid discharge could be seen. In severe situations, visual impairment may occur as a result of the cornea's dark pigment obstructing vision. The dog will go blind if the condition is not treated. The condition typically progresses rapidly in young dogs (ie, 1-5 years of age) and lesions are less severe in animals affected later in life (ie, >4-5 years of age). One to two mm in front of the leading edge of the lesion, in the clear cornea, lipid infiltrates may also be seen. Visual impairment results from the entire cornea becoming vascularized, pigmented, and opaque.

Neovascularization of a cat's cornea
Neovascularization of a cat's cornea

In dogs who may be genetically predisposed to developing CSK, high altitude and prolonged sun exposure seem to exacerbate clinical symptoms because UV radiation may alter cornea-specific antigens, which start cell-mediated inflammation.

What causes pannus?

 

Pannus is thought to be a hereditary condition that develops as the pet ages. Breeds such as German Shepherds, Belgian Shepherds breeds, greyhounds and Border Collies are the most commonly affected breeds, but pannus can occur in any breed.

Rays of light shining through clouds. Ultraviolet rays
Rays of light shining through clouds. Ultraviolet rays

Predisposing factors such as increased exposure to ultraviolet light, high altitudes, and smoke may contribute to the development of pannus and certainly can exacerbate the condition.

How is pannus diagnosed?

 

Diagnosis is based on medical history and clinical signs. Diagnostic tests include corneal staining with fluorescein, intraocular pressure testing (IOP), and corneal or conjunctival scrapings. Many of these tests are often done to rule out other eye conditions.

What is the treatment and long-term management of pannus?

 

Treatment involves using topical corticosteroids (typically prednisolone or dexamethasone) or other immune-modulating drugs such as cyclosporine or tacrolimus. On occasion, an injection of steroids under the conjunctiva may be done.


Antibiotics are sometimes required in cases that have developed a secondary infection. Due to the influence of UV lighting on the pannus, dog sunglasses (e.g., Doggles®) can be suggested to help give extra protection.


"Treatment will not cure the condition but will halt the progression and may reverse some of the changes."

3D illustration of the gene helix
3D illustration of the gene helix

All indicated therapies aim to slow disease progression, but there is no set standard practice for care. The severity and prognosis of the condition depend on a number of variables, including age at onset, altitude, sun exposure, and genetic predisposition. Lifelong therapy is also indicated.

In mild-to-moderate instances, long-term topical treatment with tacrolimus (0.02%-0.03% twice daily) or cyclosporine (0.2%-2% twice daily), with or without an additional topical corticosteroid (e.g., dexamethasone [0.1%], prednisolone acetate [1%] three to four times daily), is advised.

Similar to mild-to-moderate cases, topical treatments are advised in moderate-to-severe cases, but more frequently. For patients whose reaction to topical medicine is inadequate or takes longer than expected, subconjunctival corticosteroid injections may also be used as part of the treatment plan.


Barrels of radioactive strontium 90
Barrels of radioactive strontium 90

Advanced therapies, such as beta irradiation with strontium-90, soft x-rays (15 kV), and/or keratectomy (surgical intervention), are safe and successful for individuals with severe CSK who are refractory to medical therapy alone (i.e., drop application and subconjunctival injections). Patients treated with long-term topical anti-inflammatory drugs should be monitored closely for signs of ocular discomfort, discharge, redness, and behaviour changes and regularly examined by a veterinarian (ie, complete ophthalmic examination) to prevent corneal ulcerations or corneal infections.


Treatment will not reverse the alterations, but it will stop the condition's progression. Pannus requires lifetime therapy. It's critical to properly follow the veterinarian's instructions and give drugs regularly. Given that the illness frequently recurs throughout life, routine check-ups and vigilante behaviour are essential.

What is the prognosis for a dog diagnosed with pannus?

 

Although topical drugs work well in the majority of cases, certain dogs may need more aggressive therapies. In extreme circumstances, surgery to remove the pannus-related scar tissue may be advised to enhance the animal's vision. The illness could get worse if the required treatments are not taken as directed.

References

 

Ergin, I., Sainkaplan, S., & Şenel, O. O. (2021). Clinical assessment of chronic superficial keratitis (Überreiter’s syndrome) in dogs: A retrospective study (2012-2019). VETERINARIA, 70(2), 185-195.


Slatter DH, Lavach JD, Severin GA, Young S. Uberreiter’s syndrome (chronic superficial keratitis) in dogs in the Rocky Mountain area: a study of 463 cases. J Small Anim Pract. 1977;18(12):757-772.


Sridhar M. S. (2018). Anatomy of the cornea and ocular surface. Indian journal of ophthalmology, 66(2), 190–194. https://doi.org/10.4103/ijo.IJO_646_17


Williams DL. Major histocompatibility class II expression in the normal canine cornea and in canine chronic superficial keratitis. Vet Ophthalmol. 2005;8(6):395-400.

Ledbetter EC, Gilger BC. Diseases and surgery of the canine cornea and sclera. In: Gelatt KN, Gilger BC, Kern TJ, eds. Veterinary Ophthalmology. 5th ed. Ames, IA: Wiley-Blackwell; 2013:976-1050.

Eichenbaum JD, Lavach JD, Gould DH, Severin GA, Paulsen ME, Jones RL. Immunohistochemical staining patterns of canine eyes affected with chronic superficial keratitis. Am J Vet Res. 1986;47(9):1952-1955.

Allgoewer I, Hoecht S. Radiotherapy for canine chronic superficial keratitis using soft X-rays (15 kV). Vet Ophthalmol. 2010;13(1):20-25.

Nell B, Walde I, Billich A, Vit P, Meingasser JG. The effect of topical pimecrolimus on keratoconjunctivitis sicca and chronic superficial keratitis in dogs: results from an exploratory study. Vet Ophthalmol. 2005;8(1):39-46.

Jokinen P, Rusanen EM, Kennedy LJ, Lohi H. MHC class II risk haplotype associated with canine chronic superficial keratitis in German shepherd dogs. Vet Immunol Immunopathol. 2011;140(1-2):37-41.

Chavkin MJ, Roberts SM, Salman MD, Severin GA, Scholten NJ. Risk factors for the development of chronic superficial keratitis in dogs. J Am Vet Med Assoc. 1994;204(10):1630-1634.


Denk N, Fritsche J, Reese S. The effect of UV-blocking contact lenses as a therapy for canine chronic superficial keratitis. Vet Ophthalmol. 2011;14(3):186-194.

Höcht S, Gruening G, Allgoewer I, Nausner M, Brunnberg L, Hinkelbein W. Treatment of keratitis superficialis chronica of the dog with strontium 90 [article in German]. Strahlenther Onkol. 2002;178(2):99-104.




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