Laminitis Terminology: SIRS Rather Than Sepsis

Horse owners have long heard that laminitis can be associated with sepsis, a word that describes an overwhelming bacterial infection of the body. It came from our veterinarians and laminitis researchers, who've frequently referred to the term "sepsis" when discussing the disease, using it interchangeably with systemic inflammatory response syndrome (SIRS).

Now, said James Orsini, DVM, Dipl. ACVS, of the University of Pennsylvania's New Bolton Center for Equine Veterinary Research, veterinarians and researchers are turning to SIRS as the more appropriate term when discussing, treating, and preventing equine laminitis.

"We've used both the terms 'sepsis' and 'SIRS' in laminitis research, following a convention used in human research," Orsini said when he presented during the Laminitis News Hour at the 2012 Conference on the Equine Limb: Advanced Diagnostics and Therapeutics, held Nov. 2-3 in Monterey, Calif. As it turns out, that convention isn't a perfect analogy when it comes to horses.

SIRS describes a cascade of inflammation that frequently leads to laminar failure in the hoof. However, as the word "systemic" implies, this inflammatory response affects various body systems. That means, while our focus is often on the foot, much more is going on within the SIRS-afflicted horse. Research shows that, in these cases, subclinical inflammatory indicators are evident in the liver, lungs, and kidneys before the onset of clinical laminitis.

Orsini outlined the causes of SIRS to include:

  • Infection or endotoxemia;
  • Trauma;
  • Ischemia (restricted blood supply to tissues);
  • Immune-mediated diseases;
  • Surgery;
  • Hypo- or hyperthermia; and
  • Profound hypoxia or hemorrhagic shock (oxygen deprivation).

In the case of SIRS laminitis related to pleuropneumonia (bacterial infection secondary to pneumonia or lung abscesses), enterocolitis (inflammation of the small intestine and colon), and endometritis (inflammation of the innermost lining of the uterus), the connection to bacterial infection (or resulting sepsis) is obvious. However, SIRS can occur without evident infection or sepsis. For example, both the black walnut exposure and carbohydrate overload models of laminitis used in research settings result in SIRS-associated laminitis, but without infection or sepsis.

The switch in terminology from sepsis to SIRS might sound like simple semantics, but the change of perspective can influence how veterinarians medically view and treat horses with SIRS. Treatment focus turns to decreasing inflammation, both systematically and in the hoof, Orsini said.

Understanding inflammation's relationship to laminitis also indicates a need to identify SIRS before laminar damage occurs. To that end Orsini presented the following proposed diagnostic indicators of SIRS in adult horses:

  • A rectal temperature above 105°F or below 98°F (normal is 98.5-101.5);
  • An elevated heart rate above 60 beats per minute (normal is around 30-40);
  • Hyperventilation or tachypnea (abnormally rapid breathing); and
  • An increased white blood cell count.

Recognizing these clinical signs early and initiating prompt and vigorous treatment at the first sign might prevent or allay the progression to multiple-organ dysfunction or failure and the onset of laminitis, Orsini said.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.