Deciphering Equine Fibromyalgia Syndrome (EFMS) - The Forgotten Fungus Among Us

EFMS can present in a wide variety of ways - the particular combination of symptoms will be dramatically different from one horse to the next.

By Brenda Bishop, VMD

While the subject of Fibromyalgia Syndrome (FMS) in humans is confusing and poorly understood at best, it is even more so in horses. Different theories abound regarding every aspect of the condition, in particular its pathogenesis. Treatment can cover a wide range of approaches in people and more often than not is unsuccessful. A variety of symptom specific drugs are ultimately prescribed. It is interesting that horses with Equine Fibromyalgia Syndrome (EFMS) present with many of the exact same symptoms described by human patients. Furthermore, with regard to both species there exists a series of ongoing scientific arguments. Is FMS an autoimmune disease or an ATP (adenosine triphosphate) storage disease? Is FMS acquired or does it result from an inherited predisposition? Are the associated bacterial, viral and fungal infections primary or secondary? Whether the chicken or the egg came first, symptoms of EFMS in horses are subtle in the early stages, extreme in the later stages, easily recognizable, and in most cases easily treated with lasting good results.

A thorough history is particularly useful in making the diagnosis of EFMS in a horse or pony. Since most of the symptoms take years to develop, it helps the veterinarian if the animal has had the same owner and/or trainer for at least one year. A series of questions directed to the primary caretaker will often garner one or more of the following reports: a change in dominance within the herd (usually a shift from herd boss to bottom of the pecking order); chronic irritability or grumpiness (such as PMS-like behavior in a mare); severe depression and listlessness (standing apart from the herd); extreme anxiety and tension (the ‘high-strung’ animal); mood swings (the show horse who is hyperexcitable in the show ring but dog-tired at home); newly acquired problems walking on and off a horse trailer; problems standing quietly for the blacksmith; excessive tail swishing while in work; kicking for no apparent reason; a constant habit of ‘sneering’ at other horses and people, making faces, baring the teeth, pinning the ears and threatening to bite (typically when the handler tightens the girth of the saddle or harness); lower lip flapping; head-shaking; cribbing; an occasional loud grunting sound while working, sleeping or both. If any of these behavior patterns exist, a thorough physical exam should endeavor to uncover patterns consistent with EFMS.

It is important to remember that as in human FMS, EFMS can present in a wide variety of ways. An individual can have just two or three symptoms or as many as twenty. The particular combination of symptoms will be dramatically different from one horse to the next. Perception is everything when trying to make this diagnosis and the veterinarian has to know what he or she is looking for. Effects of various systems’ malfunctioning are not always obvious. Confusion reigns, as in people who seem normal and healthy outwardly but are totally disabled by FMS. Physicians are reluctant to make the diagnosis of FMS just because it is so poorly understood. Many opinions exist, but in horses at least, an underlying chronic systemic low-grade fungal infection is usually present. The complex and theoretical scenarios of how a fungal species comes to be so thoroughly established are another topic for research. An interesting historical fact common to both FMS and EFMS patients is that there was almost always a traumatic physical or emotional shock prior to the onset of symptoms. The classic example in horses is the gelding that had ‘a difficult castration’. Performance horses that spend much of their lives in transit or in dusty stalls, enduring too many hours in environments that are far from fungus free, are prime candidates.

For purposes of this discussion, physical exam findings in an EFMS horse can be grouped into five categories: autoimmune problems, micro-circulatory deficits, cranial nerve problems, endocrine imbalances, and generalized chronic fatigue. Unfortunately for the veterinarian, chronic fatigue can be hard to substantiate. It is probably the most common complaint in human patients, some of whom suffer from FMS and CFS (chronic fatigue syndrome). The importance of a complete history, though subjective, should be obvious. Autoimmune problems run the gamut from immune mediated arthritis to toxicity to immune mediated neuritis. The horse will give the impression of total body soreness. Arthritis can be generalized or joint specific, for example, worse in a previously injured joint or joints. Whenever a mild to moderate lameness is present that comes and goes or that shifts from front to hind or from side to side, EFMS should be high on the differential diagnosis list. Some individuals will have a ‘toxic’ appearance: abnormal fat deposits at the base of the tail and/or a pot-bellied look. Those horses that have a respiratory component might exhibit an occasional mucous nasal discharge and a very occasional non-productive cough. Others will display obvious parotid salivary gland enlargement (‘swollen glands’) particularly during rainy weather. It is not uncommon to discover some overlapping symptoms of COPD, such as flaring nostrils at rest. The owner might report ‘respiratory allergies that come and go’. Immune mediated neuritis can manifest itself as unexplained hyperextension of the hock and stifle joints (stringhalt). In the latter case, one should always check for concomitant lower cervical, thoracic or lumbar pain.

Deficits in micro-circulation, whatever the pathogenesis, lead to a multitude of problems. Stiffness along the affected horse’s topline is almost always present. Skeletal muscle deconditioning is easily recognizable at a glance: young to middle aged horses will have a prominent topline; older horses will appear sway backed. Examples of smooth muscle deconditioning are lBS (irritable bowel syndrome), LBS (leaky bowel syndrome) and poor urinary bladder tone. Cardiac muscle weakness is evidenced most commonly in humans as mitral valve prolapse; EFMS horses can exhibit moderate to severe aortic regurgitation, i.e., a loud diastolic murmur with or without left ventricular enlargement. Those areas of the horse’s body farthest from the heart are at the greatest risk for insufficient capillary perfusion. It is a well known fact that deficiencies in pulmonary function such as asthma and COPD are characterized by loss of compliance at the level of the alveoli. Similarly, any part of the integument can suffer drastic changes. Problems to look for include: a dull greasy haircoat, chronic fungal skin infections (commonly streptothricosis), a coat that ‘stands on end’, signs of localized or generalized pruritis, chronic abscesses in the feet, bruised soles, petechial redness in white hoof walls, white line disease, cracked insensitive laminae and extreme sensitivity to hard uneven ground, i.e., a hard gravel road. A classic example is the ‘thin skinned’ horse that suffers in misery every summer from a hypersensitivity to fly bites followed by chronic pruritis and topline alopecia (mane and tail).

Hypersensitivity to touch, whether insects or grooming tools, is present in about half of all cases. A smaller group will exhibit hypersensitivity to non-contact stimuli such as sound. The best example of this is the ‘lunatic’ horse that nobody will ride because he or she will ‘explode for no reason’. Another classic case is the head shaker who suffers in constant misery from hypersensitivity to light. Exactly how some cranial nerves might be involved is academic. The senses of taste and smell are next to impossible for the veterinarian to evaluate. Some people with FMS report a constant metallic taste in the mouth. Some form of myofacial pain is common to horses and humans. When the masseter muscles are affected, extremes in appetite ensue: either rarely hungry or always hungry. Many symptoms that suggest cranial nerve involvement overlap with those that could be explained by circulation deficits. The EFMS horse’s anterior pituitary is probably involved because of the wide range of endocrine imbalances frequently reported: extremely high or low estrogen, progesterone or testosterone levels, excessive sweating or anhidrosis, insomnia (which contributes to chronic fatigue) and loss of balance or equilibrium. Owners might describe stumbling, falling down, difficulty picking up one or both leads at the canter, or problems moving on uneven ground and sloping ground (such as a horse trailer ramp). Remember that common denominator in EFMS of an incident sometime in the horse’s life of a traumatic physical or emotional shock? It becomes perfectly logical that EFMS and chronic fatigue (adrenal exhaustion) syndrome should mirror each other.

According to the chronic systemic fungal infection theory, most if not all of the problems associated with EFMS can be significantly ameliorated with daily oral dosing of a fungicidal drug for a minimum of 14 days. Some individuals benefit from a longer course of treatment, up to 12 weeks. In a 2-week treatment program involving twenty horses symptomatic of EFMS, all improved either one hundred percent or nearly one hundred percent. Duration of their condition probably factored into their degree of improvement. Special consideration should be given to those horses working at extreme sports such as racing, because a certain percentage of these will exhibit exercise induced epistaxis. While not all ‘bleeders’ have EFMS, all advanced cases of EFMS are at increased risk for developing pulmonary hemorrhage when stressed. These horses should be dosed for a longer period. Attempts at culturing fungal elements from blood or any other tissue are time consuming and frustrating at best; on those rare occasions when a fungal species is cultured, it is a diagnostic challenge to differentiate between a primary pathogen and a secondary contaminant. Additionally, there is a real danger that the laboratory technician will inhale aerosolized spores. A thorough history suggestive of EFMS coupled with favorable response to a fungicidal agent supports the diagnosis. In cases where hepatic function is questionable, pre- and post-treatment serology is appropriate. Finally, on a case by case basis, suggestions should be made so as to eliminate sweet feed, molasses and any refined sugars from the diet. Prolonged use of antibiotics and especially steroids must be discouraged. Any hormone therapy by any route of administration should be avoided at all costs. Reinfection can be prevented if the owner understands how not to ‘set the stage’ for immunosuppression and fungal proliferation.

The author wishes to thank Dr. Ron Bell, Histopathology Associates, and Dr. Paul Plante for kindly reviewing this article.

© Copyright 2003 by Brenda Bishop, VMD. No portion of this work may be reproduced without express written permission of the author.

For more information:
1404 McCaskill Rd.
Carthage, NC 28327

About the author:
Brenda Bishop is a 1976 graduate of the University of Pennsylvania School of Veterinary Medicine. She operates a private equine practice in Southern Pines, NC, Sport Horse Associates. She and her husband enjoy carriage driving with a collection of retired thoroughbred race horses and their rescued Dalmatian, “Missed A Spot”.