Page 1297 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

1272 CHAPTER 12

VetBooks.ir on these cells, thereby enhancing immune function NEUROFIBROMA (SCHWANNOMA)
and targeting of melanomas. A response is indicated
by a slow decline down to 50% of pre-treatment Definition/overview
size occurring during the first 6 weeks of treatment. Neurofibroma is a tumour of peripheral nerves. It
The progression of the tumour may be halted for may occur anywhere associated with nerve sheath
months to years following cessation of treatment. tissue, but predominantly in the upper and lower
Unfortunately, cimetidine (2.5–5 mg/kg p/o q8–12 h eyelids (Fig. 12.70).
for a minimum of 16 weeks and continued for 2–3
weeks following resolution of tumour growth) has Aetiology/pathophysiology
inconsistently been shown to decrease the number Dermal or subcutaneous Schwann cells are involved.
and size of melanomas, probably owing to its poor The cause of the neoplastic change is unknown.
oral bioavailability (14%). To achieve concentrations
associated with efficacy in humans, an unaffordable Clinical presentation
dose of 48 mg/kg is required. Adding piroxicam Small (1–10 mm), hard, subcutaneous nodules are
(0.2 mg/kg q24–48 h with grain; watch for diges- present. Multiple nodules may be observed. Growth
tive issues and periodically check renal function) to of the nodules causes erosion through the overlying
cimetidine therapy may be beneficial but there are skin, allowing development into a fibroblastic-type
currently no controlled studies. lesion. Hair loss is rare until ulceration occurs.
Other non-conventional treatments include trans-
differentiation, Frankincense oil (with the anti- Differential diagnosis
tumour effects of boswellic acid), cytokine-encoding Sarcoid.
plasmid DNA (IL-18 and IL-12), a plasmid DNA
vaccine encoding Streptococcus pyogenes EMM55 pro- Diagnosis
tein injected intratumourally and a DNA plasmid Surgical removal or biopsy of non-ulcerated areas
vaccine encoding human tyrosinase (pING-HuTyr). and histopathology are diagnostic. Depending on
As the equine tyrosinase sequence has 90% homol- the pathologist, the tumour may be diagnosed as a
ogy to the human sequence, transdermal injection of neurofibroma or a sarcoid. A neurofibroma is clini-
the xenogeneic tyrosinase DNA vaccination would cally a distinct lesion and has a different clinical
be suitable for use in horses. The vaccine is admin- appearance from sarcoids located around the eyelids.
istered via a ‘needleless’ transdermal device in the
pectoral region. The vaccine protocol requires four
treatments on an every-other-week basis and booster 12.70
vaccines every 6 months. Tumour shrinkage has been
reported with vaccination, starting between 3 and
6 months, and optimal responses or complete dis-
appearance around 6–12 months. Positive humoral
responses were seen in all treated horses. Cellular
reactivity was noted, with tumour- infiltrating lym-
phocyte populations identified, with a statistically
significant increase in CD8+ lymphocytes along with
a decrease in CD4+/Foxp3+ regulatory T cells fol-
lowing vaccination. This xenogenic vaccine appears
to be safe and well tolerated in horses.

Prognosis Fig. 12.70 Neurofibroma is most commonly
The prognosis is guarded. A slightly more cautious found on the upper and lower eyelids as small hard
prognosis should be given for grey horses, even subcutaneous nodules, with hairless areas around the
though the majority of ‘black’ lumps are benign. tumour, similar to sarcoid.