Blepharitis in dogs: causes, diagnosis and treatment
Periocular lesions in dogs are very common in routine veterinary practice. However, there are many underlying causes, so knowledge of the various diagnostic methods and respective treatments of blepharitis in dogs is essential.
Blepharitis in dogs: aetiology and risk factors
Inflammation of the eyelids, also known as blepharitis, is a process with a multiple, wide-ranging aetiology that should be treated as a dermatological disorder. The inflammation affects the cutaneous tissue and normally without any compromise to the inner layers of the eye.
The causes of this clinical finding can be divided into primary,1 which are directly related to alterations of the meibomian glands or the glands of Zeis and Moll; and secondary, which can subsequently be categorised as:
● Infectious causes: mainly involving bacterial agents, in particular Staphylococcus aureus.2
● Immune-mediated causes: blepharitis is frequently observed in dermatological disorders such as lupus or pemphigus. Pemphigus vulgaris3 affects the patient’s mucocutaneous junctions, where various lesions such as vesicles, blisters or collarettes can be found, in addition to inflammation. Lupus causes generalised changes to the skin and can also affect the eyelids.4
● Parasitic causes: on the one hand, ectoparasites,5 such as Sarcoptes scabiei or Demodex canis, trigger inflammatory reactions by either excavating galleries in deep layers of the skin or altering the hair follicles, respectively. On the other hand, endoparasites, such as Leishmania infantum , may cause ocular and periocular lesions6 in dogs. For example, 24.4% of animals with Leishmaniasis suffer from the aforementioned disorders.
● Fungal causes: typically Microsporum canis, Microsporum gypseum, Trichophyton mentagrophytes and Malassezia spp.
● Seborrhoeic blepharitis: associated with the accumulation of fat on the scalp which accumulates on the eyelids.
● Blepharitis due to an environmental and/or food allergy.
● Genetic predisposition: certain breeds of dogs, such as brachycephalic dogs, can suffer skin disorders which may affect the eyelids giving rise to blepharitis.
Clinical signs and diagnosis
Patients with blepharitis manifest several clinical signs, notably processes such as scaling, hyperaemia. alopecia and oedema which all course with a range of cutaneous lesions: papules, macules, pustules, pruritus, scabs, ulcers and the associated pain.7
As discussed in the previous section, blepharitis is a multifactorial process with diverse causes, so it is essential to carry out a differential diagnosis to establish the appropriate and optimal therapeutic protocol.
First of all, the patient’s clinical history plays a major role, given that the time of year when the alteration occurs, the location of the home and the frequency of presentation of lesions can all help direct the veterinary surgeon’s diagnosis with regards to allergic and parasitic causes.
A thorough differential diagnosis8 requires skin scrapings, trichograms, dermatological cytology and histology.These techniques combined with microscopy can confirm the presence of different kinds of ectoparasites, fungi, yeasts and bacteria. However, a negative result in these tests should not completely rule out a particular disorder, as there are cases, such as sarcoptic scabies, where 50–70% of scrapings collected yield negative results.
To rule out other diseases, laboratory techniques including blood tests, serology for certain parasites, e.g., Leishmania infantum, and allergy tests should be used to produce a full differential diagnosis.
Treatment
The therapeutic protocol9 varies given the wide range of aetiologies associated with blepharitis. Which is why the diagnosis must be as accurate as possible. Due to the location of the lesions, most medications used to treat blepharitis are administered systemically.
First of all, the clinical signs should be mitigated with anti-inflammatories and coverage antibiotics to avoid secondary infections, bearing in mind that if a bacterial culture is performed, then the antibiotic that acts on the pathogen should be administered.
In patients with immune-mediated diseases, the use of corticotherapy is essential for their improvement, establishing an initial dose and then a gradual stepwise dose reduction.
Finally, medicines antiparasitic agents and antifungals, both therapeutically and preventively, especially with antiparasitic agents, are all necessary to deal with ectoparasitism and mycosis, as is thorough hygiene in the animal’s environment.
Conclusions
Blepharitis in dogs is a disorder with multiple causes and a variable clinical picture. Thus, there is no single treatment and a differential diagnosis must be performed to determine the original cause of the process.
