THE DIAGNOSIS OF
SAID can be diagnosed at an early stage before horses experience
the scourge of persistent coughing and labored breathing, and worse, permanent lung
scarring. At this early stage, no single test is perfect for diagnosis, so tests
are employed together.
- Physical examination
- Bronchoalveolar lavage.
- Lung function test
- Chest X-ray.
In many cases, physical examination (lung
auscultation, etc), endoscopy, and chest X-rays are normal in horses with early SAID, yet
the horse isn't peforming well. That's why more sensitive tests are necessary, such as
bronchoalveolar lavage (BAL) and lung function tests. More complete descriptions of BAL and lung function tests
can be found in this website.
Diagnosis of SAID in the context of the 'poor
SAID can be diagnosed during the evaluation of horses for poor
performance. In the workup of such a vague complaint, a number of tests can be used, but
only a few help with the diagnosis of SAID. BAL and lung function testing, including
a histamine challenge are the most sensitive measures currently available for diagnosing
- Endoscopy: SAID
horses may have mucus flecks or blobs in the trachea, especially obvious
after exercise. However, not all horses with mucus have SAID.
- Endoscopy during exercise: SAID horses fade early during intense exercise on the
- X-rays of the chest: SAID
horses may have a bronchointerstitial pattern. In many cases X-rays are normal or
indistinguishable from normal.
- Lung function tests: Baseline
lung function tests are often normal, but one can see increased lung resistance, or
frequency dependence of resistance (see Lung
- Histamine Challenge: Airways
are hyper-reactive to histamine when administered as an aerosol. The
reason for this is unclear, but persistent inflammation and airway wall thickening are
likely causes. Below is shown a horse with a facemask, receiving histamine by nebulizer,
during a test of airway reacivity. See Lung
nebulization during test for airway reactivity
- Bronchoalveolar lavage: Saline
pushed into the lung is recovered by suction, and the cells within this fluid are
evaluated: increased numbers of mast cells, neutrophils, or eosinophils
(rarely) are seen in SAID.
- Exercise testing (metabolic stress test): This is a test of aerobic capacity. VO2max (maximum oxygen
consumption), blood lactates, heart rate response, and distance & speed traveled
before fatigue are measured. Exercise testing can tell you if your horse is in shape and
ready for performance.
stress test on the high-speed treadmill at Tufts University School of Veterinary Medicine
- Muscle enzymes: elevations
in creatine phosphokinase (CK) or aspartate transaminase (AST) point towards muscle
damage, a common cause of stiffness, particularly in young fillies. CK is not
specifically elevated in horses with SAID.
- Nuclear medicine scan: For
diagnosis of early orthopedic problems (bone remodeling disease, stress fractures) or
muscle tears as a cause of lameness. Used in conjunction with a standard
in-hand lameness exam and X-rays. Not a specific diagnostic tool for