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Lost in the Fog
UC-Davis veterinarians battle a rare case of lymphoma; racing icon euthanized in mid Sept.


DVM360 MAGAZINE


When the primary splenic mass was first found, splenectomy was contemplated. Clinical splenectomy in the horse is rare and more commonly performed for research. Several are done every year for USDA research projects with WSU and the University of Idaho, and at Iowa State University's College of Veterinary Medicine. Splenectomy is challenging because of the large size of the horse's spleen, the location within the abdomen, and the fact that it is a blood-storing organ and has a propensity toward hemorrhage.

According to Reinertson, who has done several, it is best performed by resection of the left 16th rib and incision of the diaphragm. The large size of Lost in the Fog's spleen (with tumor involvement) would have made it even more difficult. Ideally, selection of subjects "who were healthy but had easily palpable ribs significantly increased the ease of performing the splenectomy, decreased the duration of the surgical procedure and decreased the incidence of postoperative complications."

The long-term prognosis with lymphoma is usually very poor. Treatment with combinations of chemotherapy agents has provided some improvement in the form of suppression of the disease for varying periods of time. Horses with lymphoma limited to the skin may survive much longer than those with internal involvement.

"We are trying to shrink the tumors," Gilchrist says prior to the euthanasia. If they can shrink them significantly, possibly they can be removed surgically.

Upon arriving at Golden Gate Fields, Fog was put on mild pain medication and dexamethasone to try and decrease tumor mass size. After about two weeks, blood work and ultrasound revealed no changes, and the decision was made to begin several weeks of chemotherapy treatments. The chemotherapy, to be done at UC-Davis, consists of up to six sessions, three weeks apart. The horse will go to the university for the treatments and return home to Golden Gate.

"Chemotherapy is a rational treatment for any multicentric malignancy," states Robertson, "though no successful medical treatment of this tumor exists (in horses)." According to veterinary literature, although methotrexate and dexamethasone have been tried for short periods, and have reduced the size of lesions for short time periods, animals were eventually euthanized when tumors re-grew.

Though veterinary oncologists have insufficient clinical data to state that chemotherapy treatment of lymphoma is ineffective, Robertson believes that "more aggressive therapy administered for longer periods of time may show some benefit in individual horses."

Fortunately, effects of chemotherapy in the horse are not as dramatic in the horse as they are in the human (hair loss, etc). The hair cell growth cycle includes the growing (anagen) stage, the resting (telogen) stage and the transitional (catagen) stage. At the end of the telogen stage, the hair falls out. Chemotherapy drugs kill all rapidly growing cells, and so the hair bulb cells are vulnerable. In humans, chemotherapy drugs weaken or kill developing hair, though in the horse, for some unknown reason, this does not occur.

The cause of the lack of alopecia response to chemotherapy in the horse is unknown, though Bain speculates that it might be because of the physiology of the growth cycle of the equine hair cells, or to a lack of effect of the drugs used.

Even though the horse's hair coat is unaffected, monitoring of the blood work is most important since these drugs will affect rapidly dividing cells, usually those in the bone marrow, resulting in a low white blood cell count, which creates a susceptibility to secondary infections (pneumonia, diarrhea). The spectre of laminitis loomed as well.

On Aug. 23, Lost in the Fog was walked and given some of the carrots and apples that had been left for him by his many fans.

The horse's health took a turn for the worse, however. Lost in the Fog was humanely euthanized on Sept. 17.

While at University of California-Davis, Lost in the Fog was attended to by a team of veterinarians. Assisting primary overseer Dr. Gary Magdesian, in addition to Dr. Larry Galuppo, are Mary Beth Whitcomb, DVM, Head Equine Ultrasound; Julie Dechant, DVM, MS, DACVS; Dr. Alain Theon, DVM, MS, DACVR, Chief of Equine Radiation and Medical Oncology; and residents Johnathan Anderson, BVM&S; Carrie Finno, DVM; and Emily Haggett, BVSc.

Those that worked with Lost in the Fog pointed out that his heart was key to his treatment.

"The fact that he is bright and bold despite his medical condition," Magdesian says, "is probably the same quality that allowed him to become such a great racehorse."


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Source: DVM360 MAGAZINE,
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