- Definition
- Pathophysiology
- Systems Affected
- Genetics
- Incidence/Prevalence
- Geographic Distribution
- Signalment
- Signs
- Causes
- Risk Factors
BASICS
Dermal fibroblast neoplasm with a minor epidermal component, with a variety of clinical forms. Often locally aggressive with a high propensity for recurrence after surgical excision, but does not metastasize.
Incompletely characterized, complex, and multifactorial:
- BPV infection BPV infection potentially causal:
- BPV DNA detected within fibroblast nuclei in most sarcoids, and at low levels in epidermis in some sarcoids (BPV-1 most commonly, also BPV-2, BPV-13, and horse-specific BPV-1 variants)
- Viral proteins (e.g. oncoproteins E5, E7) consistently detected
- BPV-1 DNA also detected in skin and blood of healthy horses
- PV virions not detected via electron microscopy or virus isolation in sarcoids
- BPV inoculation does not reproduce persistent disease
However, viral involvement unconfirmed:
- Environmental factors also implicated
- Epizootic disease outbreaks occur, with apparent transmission between horses
- Insect transmission likely (identical BPV-1 DNA in sarcoids and flies in same regions)
- Worldwide occurrence without seasonal or geographic predilection suggests other transmission routes (e.g. direct wound contact, indirect fomites)
Genetic susceptibility to sarcoids suspected, and a polygenic inheritance pattern proposed:
- Higher risk in some breeds and families
- Increased risk linked to MHC I genes (e.g. ELA-A3), MHC II genes (ELA-W13), and MHC II and non-MHC genes on ECA-20, ECA-22 (involved in host immune response)
Most common neoplasm of horses, with a prevalence of 1–12% reported, and accounting for 15–65% of all neoplasms, ahead of SCC, melanoma, and papilloma.
- Higher risk—Quarter Horses; possibly Appaloosas, Arabians, and Thoroughbreds
- Lower risk—Standardbreds
Single or multiple lesions in a variety of body regions; may occur at sites of previous injury. May progress into more aggressive forms spontaneously.
- Most frequent on the head (pinnae, lip margins, periocular), neck, lower limbs, and ventral body (inguinal, preputial, perineal)
- Clinical forms are variable, and often mixed, including:
- Occult—focal, roughly circular, non-raised areas of alopecia with foci of scaling, lichenification, or papules. May start with subtle hair color/quality change. May be more common in relatively hairless body areas. May remain static for years, slowly enlarge, or progress to verrucous forms
- Verrucous (warty)—irregular papillomatous and scaly plaques to peduncles, often surrounded by a zone of mild lichenification with altered coat quality. May be less common on the limbs except for coronary band areas. Slow growing
- Nodular—firm, well-defined dermal or subcutaneous nodules of variable size (≥0.5–20 cm). May be solitary, or in small to occasionally myriad clusters. Predilection sites include inguinal, preputial, and periocular areas
- Nodular and ulcerated (“fibroblastic”)—irregularly nodular locally invasive lesions with prominent ulceration and exudation, often resembling exuberant granulation tissue (“proud flesh”). Fly worry, myiasis, and bacterial infections commonly complicate
- Malevolent—rare, invasive, irregularly nodular lesions that can infiltrate lymphatics and potentially local lymph nodes
Likely caused by a complex association between BPV and inheritable traits of the horse, with environmental influences.
DIAGNOSIS
TREATMENT
MEDICATIONS
FOLLOW-UP
MISCELLANEOUS