Newly published study examines equine multinodular pulmonary fibrosis

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Equine multinodular pulmonary fibrosis (EMPF) is a lung condition in horses in which scar tissue forms throughout the lungs, creating diffuse miliaries or nodular pulmonary patterns on radiographic imaging. Experts believe that equine herpesvirus-5 (EHV-5) could also be associated with EMPF because similar viruses have been known to cause lung issues in humans and mice. However, not all cases of EMPF are caused by EHV-5, as some horses with EMPF-like symptoms don't test positive for the virus.¹

A newly published study in the Journal of Veterinary Internal Medicine researched EMPF and specifically the prognostic indicators for the disease since current clinical literature is limited.. The horses involved in this study consisted of 24 (52%) mares, 21 (46%) geldings, and 1 (2%) stallion, totaling to 46 horses. The median age was 15 years from a range of 5-26 years and horses came from 9 different clinics spanning across the United States, Canada, Spain, Switzerland, and the Netherlands.¹

Prior to the study each horse was diagnosed with EMPF by a diplomate of the American College of Veterinary Internal Medicine or the European College of Equine Internal Medicine, all specializing in large animal medicine.¹ Researchers on the clinical study confirmed the diagnosis in 34 out of 46 cases by examining lung tissue either from biopsies or autopsies. In 12 other cases, lung tissue could not be examined directly, so researchers relied on clinical symptoms, like respiratory disease and abnormalities seen on lung scans, while also ruling out bacterial infections.¹

Overall the study found that diagnostic factors of EMPF in these participants were weight loss (36/46, 78%), difficulty breathing (33/46, 72%), rapid breathing (32/46, 70%), and fever (18/46, 39%), however researchers indicated that fever is not a reliable sign of EMPF.¹ Researchers also found that more horses with EMPF had abnormal cells in their respiratory fluid compared to horses with asthma.

Prognostic outcomes remain poor for this disease. During hospitalization, 19 out of 46 horses (41%) were either euthanized or died. The main reason for euthanasia was a poor prognosis (10/46, 22%), followed by the disease getting worse despite treatment (4/46, 9%). Two horses (4%) had complications such as colic, diarrhea, and laminitis, leading to euthanasia. One horse suffered from acute respiratory distress and died, while another owner declined treatment and requested euthanasia. One additional case did not provide a reason for euthanasia.¹

Among the 27 horses that survived in the short term, 1 was lost to follow-up within 3 months. Eleven out of 45 horses (24%) survived for at least 3 months. Additionally, 15 out of 45 horses (33%) either died or were euthanized within 3 months after leaving the hospital.¹

In conclusion, the researchers aimed to provide further insight into the prognosis of this disease, maintaining its poor outlook. Furthermore, corticosteroid treatment does not improve the 3-month survival time seen in most participants.

Reference

Craven A, Todd-Donato A, Stokol T, et al. Clinical findings and outcome predictors for multinodular pulmonary fibrosis in horses: 46 cases (2009-2019). J Vet Intern Med. Published online April 15, 2024. doi:10.1111/jvim.17084