Much remains unknown about vitiligo in horses – case report

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The horse's lip region, four years apart, with the earlier image at left. Images: Fonteque et al. https://doi.org/10.1590/1678-4162-11792
The horse’s lip region, four years apart, with the earlier image at left. Images: Fonteque et al. https://doi.org/10.1590/1678-4162-11792

The curious nature of vitiligo is discussed in a scientific paper that followed the disease in a roan horse over a four-year period.

Vitiligo is a skin disease that affects both animals and humans. It is characterized by depigmentation.

The case in the 18-year-old roan gelding was unremarkable in many ways, but that only highlights that much remains unknown about the cause and progression of the disease.

Vitiligo, involving full or partial destruction of melanocytes in the skin and associated hair follicles, leads to the formation of white prominent spots on the surface.

Some areas are more prone to depigmentation, including around the anus and genitals, and facial areas, especially the nose and around the eyes and lip surroundings.

The cause is not completely clear. It could be an inherited condition, an acquired disease, or of autoimmune origin.

Researchers, writing in the journal Arquivo Brasileiro de Medicina Veterinária e Zootecnia, noted that 0.5 to 1% of people have the condition. In contrast, there is little to no data regarding horses. However, a clinic in the United States has reported a 0.7% disease prevalence in equines.

The vitiligo four years apart, with the earlier image at left.
The vitiligo four years apart, with the earlier image at left.

The 340kg horse at the center of the case study was involved in a university extension program in which it pulled a cart for three hours a day for the collection of recyclables.

The depigmented regions were observed on the animal’s face during a routine clinical examination at the veterinary hospital at Santa Catarina State University in Brazil. The condition was monitored for four years.

The lesions ranged from 0.5cm to 4cm in diameter. There appeared to be no itchiness, nor were there any scabs or secretions.

The initial physical examination of the horse was otherwise unremarkable, apart from an elevated heart rate and fast breathing, which the researchers put down to agitation.

Four biopsy samples were examined microscopically, showing low pigmentation of the epidermal basal layer due to the complete absence of epidermal melanocytes. The lesion areas displayed a moderate amount of melanin-filled melanomacrophages on the superficial layers of the dermis, suggesting a clinical diagnosis of vitiligo.

The depigmentation seen around the eye, four years apart.
The depigmentation seen around the eye, four years apart.

“For this clinical case, no treatment was carried out, and the equine in question was simply monitored for four years,” Joandes Henrique Fonteque and his fellow researchers said.

During the disease course, there was a reduction in the size of some patches, increases in others, and a new depigmented area appeared near the lower lip.

The authors said there is much speculation regarding the cause and progression of vitiligo. Some scientists suggest that multiple factors are involved.

They said vitiligo has a genetic correlation with melanoma. Both occur most often in grey horses, and this relationship with the color of the coat indicates that there is a inheritance component in the condition.

Vitiligo, they said, is easy to diagnose because of the visible skin lesions, which can be backed up with a microscopic examination.

“During the course of the disease, lesions can either increase or diminish in size. The appearance of new depigmented regions is also expected. “Overall, this disease does not display alterations to organism functionality, only aesthetic changes,” they said.

Treatment plans may vary from case to case, and occasionally are even ruled out, they said.

The authors were all affiliated with Santa Catarina State University.

Vitiligo in equine: a four-year case study of a roan horse ˗ case report
J.H. Fonteque, T.C. Valente, G.M. Avila, T.G. Cristo, L.M.A. Pereira, M.S. Casa, L.C. Vincensi, R.A. Casagrande
Arq. Bras. Med. Vet. Zootec. 73 (01), Jan-Feb 2021, https://doi.org/10.1590/1678-4162-11792

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

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