Man­ag­ing a rare skin dis­ease

EQUUS - - Eq Consultant­s -

Q:My Paint geld­ing, Trooper, was di­ag­nosed with pem­phi­gus fo­li­aceus in Jan­uary 2014, and since then we’ve been on a bit of a roller coaster man­ag­ing this rare skin dis­ease, but we are not giv­ing up. I’ve been try­ing to learn more about this con­di­tion. How­ever, there is very lit­tle in­for­ma­tion avail­able (and I agree that re­search money is bet­ter spent on more common ail­ments like colic and lamini­tis). We own­ers of horses with this con­di­tion may be few and far

be­tween, but I bet we’d all like to learn more about it. Can you help? Kelly San­ford Fort Ed­ward, New York

A:Pem­phi­gus fo­li­aceus (PF) is an au­toim­mune disorder in which the body’s im­mune sys­tem at­tacks the pro­teins that ad­here to­gether the cells of the skin sur­face (the epi­der­mis). As th­ese epi­der­mal cells come “un­stuck” from each other, blis­ter­ing de­vel­ops, which turns into crusts and hair loss. The crust­ing fre­quently starts on the face and legs and then be­comes gen­er­al­ized over the body. Crusts may also oc­cur only on the coronary bands. The le­sions can be painful.

Pe­riph­eral edema (“stock­ing up”) is also common, and th­ese horses are likely to have a low-grade ane­mia (lower than nor­mal num­bers of red blood cells) as well as leuko­cy­to­sis (an el­e­vated count of white blood cells). Horses may also de­velop fever, de­pres­sion, lethargy and oc­ca­sion­ally weight loss.

The cause of the dis­ease is un­known. Here at the Univer­sity of Cal­i­for­nia–Davis, PF is the most common cause of non­in­fec­tious crusts in horses, and it is the sec­ond most com­monly seen au­toim­mune skin dis­ease in the horse, after pur­pura0 hem­or­rhag­ica. Ear­lier stud­ies sug­gested that PF might be bi­modal, de­vel­op­ing only in horses younger than a year old or in those over the age of 8. How­ever, we have since found that PF can oc­cur in horses of any age.

Like­wise, our cases here at UC– Davis do not support a pre­vi­ous as­ser­tion that Ap­paloosas are pre­dis­posed to PF. It can de­velop in horses of any age, gen­der or breed; we have seen the con­di­tion in horses, ponies and Minia­ture Horses, and it has been re­ported in don­keys. One re­cent re­port from France de­scribed a don­key whose PF oc­curred, then re­gressed, dur­ing two of her five preg­nan­cies.

In­ter­est­ingly, the cases we’ve seen here did sug­gest a sea­sonal on­set of PF---more than 80 per­cent de­vel­oped be­tween Septem­ber and Fe­bru­ary.

A biopsy is nec­es­sary to di­ag­nose PF and to dis­tin­guish this dis­ease from other con­di­tions that cause sim­i­lar­look­ing crusty, hair­less le­sions, in­clud­ing in­sect hy­per­sen­si­tiv­ity and bac­te­rial or fun­gal in­fec­tions, such as ring­worm. PF is not con­ta­gious.

PF is treated with drugs that sup­press the im­mune sys­tem. Cor­ti­cos­teroids, such as pred­nisolone and dex­am­etha­sone, are of­ten used, although th­ese must be ad­min­is­tered cau­tiously be­cause they can have se­ri­ous side ef­fects, in­clud­ing lamini­tis0. Of­ten we’ll start on higher doses to at­tempt to bring the dis­ease un­der con­trol, then ta­per off to a main­te­nance dose.

Anec­do­tal re­ports state that a gold salt (au­roth­ioma­late) can be help­ful, ad­min­is­tered once weekly un­til the le­sions wane, and then monthly there­after. How­ever, this drug is ex­pen­sive, and it also car­ries a slight risk of se­ri­ous side ef­fects, in­clud­ing kid­ney dis­ease.

Another im­muno­sup­pres­sant drug that might be help­ful is aza­thio­prine, which is used for var­i­ous au­toim­mune skin dis­eases in horses. A low platelet count is one pos­si­ble side ef­fect of this drug; how­ever, I have used aza­thio­prine in­ves­tiga­tively in eight healthy horses with no dele­te­ri­ous ef­fects. I use this drug, which is ad­min­is­tered daily, to even­tu­ally de­crease the amount of cor­ti­cos­teroids needed. It costs ap­prox­i­mately $300 per month for an av­er­age adult horse.

The prog­no­sis for PF is guarded un­til we see how the horse re­sponds to the med­i­ca­tions. The goal is al­ways to achieve full re­mis­sion of the clin­i­cal signs, but treat­ment is life­long in at least 75 per­cent of af­fected horses. Some horses with this dis­ease can be rid­den, de­pend­ing on whether long- term med­i­ca­tions are needed and where the le­sions are on the body (the sad­dle and girth area ver­sus the face or legs).

Per­haps as many as 25 per­cent of horses can even­tu­ally be taken off of all med­i­ca­tions, although re­cur­rence is a pos­si­bil­ity. Prob­a­bly 20 per­cent are eu­tha­na­tized, ei­ther be­cause they have not re­sponded to drug treat­ments or due to side ef­fects such as lamini­tis.

Stephen D. White, DVM, DACVD

Univer­sity of Cal­i­for­nia–Davis, Davis, Cal­i­for­nia

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