Spinal Cord Hamartomatous Myelodysplasia in 2 Horses With Clinical Neurologic Deficits.

Two horses euthanized for neurologic deficits were diagnosed with hamartomatous myelodysplasia of the spinal cord. One was a 5-week-old Holsteiner colt exhibiting spasms of muscle rigidity in the extensor muscles of the limbs and epaxial muscles, and the other was a 3-year-old Thoroughbred colt exhibiting progressive ataxia and hypermetria in the pelvic limbs. Each had focal disorganization of the white and gray matter of the spinal cord forming a mass interspersed with neurons, glial cells, and disoriented axon bundles. In the Holsteiner colt, the mass was at the level of C5 and included islands of meningeal tissue contiguous with the leptomeninges. The mass occluded the central canal forming hydromyelia cranial to the occlusion. In the Thoroughbred colt, the mass was at the level of L1 on the dorsal periphery of the spinal cord and did not involve the central canal.

Macrolide-induced hyperthermia in foals: Role of impaired sweat responses.

REASONS FOR PERFORMING STUDY: The mechanism of hyperthermia, a potentially fatal adverse effect of erythromycin treatment of foals, is unknown. OBJECTIVES: To determine the cause of erythromycin-associated hyperthermia. It was hypothesised that the normal sweat response of foals is impaired by treatment with erythromycin. STUDY DESIGN: Blinded, crossover study in 10 healthy pony foals. METHODS: Foals kept in stalls were given either erythromycin (25 mg/kg bwt orally, 3 times daily) or control for 10 days then turned out for a further 10 days. Quantitative intradermal terbutaline sweat tests were performed on Days 1 (baseline), 3, 10 and 20. The effects on terbutaline-induced sweating of erythromycin, terbutaline concentration and treatment day were analysed by repeated-measures ANOVA with Bonferroni-corrected pairwise post hoc comparisons. Peak temperatures were compared by Wilcoxon's signed rank test and proportions by McNemar's related samples test. Significance was set at P<0.05. RESULTS: There were significant 2-factor interactions for treatment × terbutaline after baseline, treatment × day at every terbutaline concentration, and day × terbutaline for erythromycin (P<0.001) but not control (P = 0.9) treatment. Sweating was significantly reduced from baseline in erythromycin-treated foals at all subsequent days. Erythromycin-treated foals produced less sweat at all time-points than did control-treated foals (P<0.05). Peak rectal temperatures of erythromycin-treated foals were significantly higher (P = 0.02) than those of controls. During the first 3 days outside more erythromycin-treated than control-treated foals required treatment for hyperthermia (6 vs. 0; P = 0.03). CONCLUSIONS: We believe drug-induced anhidrosis is the likely cause of hyperthermia in some foals treated with erythromycin.