Sebaceous adenitis in rabbits

 

Esther van Praag, Ph.D.

 

 

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Warning: this file contains pictures that may be distressing to some persons

 

The etiology of sebaceous adenitis also called inflammation of the sebaceous glands - is not well understood; it is considered idiopathic, inherited or endocrine. In rabbits, the disorder appears to have an inherited autoimmune origin, accompanied by a defect of the fatty acids metabolism. An autoimmune origin also established in dogs, after immunohistological analysis of skin samples, but also from the successful treatment with cyclosporine, an immunosuppressant drug.

Clinical characteristics

The first clinical manifestations of sebaceous adenitis resemble those of skin allergy: inflamed sebaceous gland with progressive destruction of the glands and the adjacent hair follicles, accompanied by inflammation of the hair follicles (mural lymphocytic folliculitis). The condition worsens over time. Hair growth stops, the fur is thinning, and alopecic patches appear. The skin becomes erythematous, with abnormal thickening (hyperkeratosis). Scales adhere tightly to the skin. Infiltration of lymphocytes into the basal layer of the epidermis (interface dermatitis) is furthermore observed in rabbits. This causes changes in the basal cells of that layer, necrosis of keratinocytes and occasionally inflammation of the follicular-dermal interface (interface folliculitis).

ebaceous adenitis in rabbits can occur in patches or be progressive, starting with non-pruritic scaling on the head. It later spreads to the neck, the pelvic region, and the rest of the body. Lesions are often symmetrical over the head and abdomen.

Three forms of sebaceous adenitis have been identified in rabbits:

Type 1: Few patches of scaly skin in a region of the body:

Sarah Davoli

 

Coco, older rabbit suffering from a few local patches of scaly skin in the pelvic region. A biopsy confirmedsebaceous adenitis.

Type 2: Generalized loss of fur over all the body and extensive scaling of the alopecic regions. This type is often associated to thymoma, a tumor originating from the epithelial cells of the thymus.

Nancy LaRoche

 

Jenny with confirmed sebaceous adenitis all over her body

Type 3: In rabbits belonging to the rex breed, more rarely in other rabbits, a smooth type of sebaceus adenitis is observed, The skin becomes alopecic, with minimal or no scaling of the skin, and without development of crusts.

 

Tal Saarony

 

Pashosh, an 11.5 year old Mini-Rex rabbit with suspected smooth sebaceous adenitis at the base of the ear region. A biopsy has not been taken due to her age, but bacterial and fungal (yeast) dermatitis as well as the presence of skin parasites have all been ruled out.

Diagnosis

Inflammation of the sebaceous glands is often mistakenly diagnosed as skin allergy. As a result, it is treated inappropriately. Skin problems such as fungal dermatitis, parasitic infestation or defluxion will often be considered, when the proposed skin allergy treatment fails to bring an improvement. This skin condition should furthermore be differentiated from thymoma-associated exfoliative dermatitis, cutaneous lymphoma, or dermatitis caused by autoimmune hepatitis.

To avoid unnecessary distress of the rabbit, it is, therefore, important to do a biopsy of the skin. Microscopic analysis with the skin sample will confirm the presence of orthokeratotic hyperkeratosis, a rare intact sebaceous glands, destructed or absent sebaceous glands and mural lymphocytic folliculitis. Radiography of the chest will rule out thymoma.

Treatment

There is no treatment for sebaceous gland inflammation, except good care. In dogs, this problem is treated by cleaning the skin with a detergent soap twice a week/month, clean its skin, followed by an application of a chlorhexiderm solution, and baby oil. This helps loosen the skin dandruff and provides the necessary fat to the skin.

A regular brushing also helps to remove the dandruff, which is a source of secondary bacterial infection.

Treatments with an antifungal, corticosteroid or an immunosuppressant drug did not bring improvement. The administration of fatty acids, vitamin A or retinoids (e.g. isotretinoin, etretinate) can be attempted, but the toxicity of these compounds must be taken into account.

The combined administration of cyclosporine (5 mg/kg, PO, sid), medium chain triglycerides and essential fatty acids, accompanied by topical application of propylene glycol (spray) was successful in the treatment of sebaceous adenitis in a rabbit. Two months later, remission was observed, with new hair growth.

Since cyclosporine is an xpensive drug, mycophenolate has been successfully administred to affected rabbits in order to reduce the inflammatory reaction. After a loadind dosis of 42mg/kg twice a day PO, it was continued at a dosis of 10mg/kg BID, accompanied by the use of skin moisterers to remove the crusts and soften the skin.

Further options include the administration of omega-3 fatty acid supplements. Since this treatment is costly, euthanasia should be considered as a humane alternative, so as not to unnecessarily prolong the rabbit's pain and suffering.

If secondary bacterial infections develop, it should be treated with antibiotics and/or an antibiotic cream (e.g. Fucidic acid cream).

 

Lulu

Healthy

After developing sebaceous adenitis

 Details from affected skin

Lyne Lavigneur

 

Jenny

Confirmed sebaceous adenitis

Ventral view of the abdomen

Top of head

Nancy LaRoche

 

Bella

Confirmed sebaceous adenitis associated to thymoma

Side view of the head

Top of head

.

Nancy Martin

 

A few months after radiotherapy, Bella developed a strange gait...

 

Video made by Debbie Hanson

 

Thymoma is associated with polymyositis in cats. Their gait is modified, stiff, stilted, affecting all limbs, with generalized muscle atrophy and muscle hyperesthesia.

 

The development of this stiff gait is also observed in rabbits that suffer from primary idiopathic sebaceous adenitis, without presence of thymoma. Here Molly.

 

 

Video made by Christie H. Paylor

 

 

Smits B, Reid MM., Feline paraneoplastic syndrome associated with thymoma. New Zealand Veterinary Journal, Volume 51, Issue 5, pp 244-247, Oct 2003 

 

For detailed information on sebaceous adenitis in rabbits,

see: Skin Diseases of Rabbits, by E. van Praag, A. Maurer and T. Saarony

408 pages, 2010.

 

 

Acknowledgements

A special thanks to Sarah Davoli, Lyne Lavigneur, Nancy LaRoche, Nancy Martin and Debbie Hanson for sharing the pictures of their rabbits Coco, Lulu, Jenny, and Bella, suffering from sebaceous adenitis.

 

Further reading

1.      Florizoone K. Thymoma-associated exfoliative dermatitis in a rabbit. Vet Dermatol 2005;16:281-284.