Jill Beech

Cytology of Tracheobronchial Aspirates in Horses

Tracheobronchial aspirates were obtained from 27 normal horses and from 57 horses with respiratory disease. Aspirates from normal horses contained mainly ciliated columnar epithelial cells, mononuclear cells, a few neutrophils and mucus. Aspirates from horses with acute suppurative bronchopneumonias or chronic bronchiolitis had predominantly neutrophils and usually large amounts of mucus; in severe suppurative inflammatory diseases, many of the cells were degenerated, and there were coils of fibrinous material resembling Curschmanns spirals. Eosinophils were rarely found, even from horses with histories suggestive of allergic respiratory disease. Aspirates from horses with epistaxis frequently had macrophages with intracytoplasmic green globules (hemosiderin). Tracheobronchial aspirates occasionally revealed subclinical lung disease. Four horses with no clinical signs of lung disease and lungs that were unremarkable on percussion and normal on auscultation had aspirates suggestive of inflammation; histologic examination confirmed bronchiolitis.

Toxoplasma-like Encephalomyelitis in the Horse

Eight horses with progressive neurologic signs had encephalomyelitis associated with toxoplasma-like protozoan bodies. There were scattered hemorrhagic, malacic lesions in white and grey matter in the brain and spinal cord. Microscopically there was malacia, mononuclear cell infiltration, especially perivascularly, gliosis, and various degrees of necrosis and hemorrhage. Other tissues were normal, except for the lung of one horse that had focal bronchopneumonia. The cerebrospinal fluid did not contain measurable amounts of IgM, IgG, or IgA. Serum from one horse was negative at 1:64 by the hemagglutination-inhibition test for toxoplasma antibodies.

Evaluation of plasma ACTH, α-melanocyte–stimulating hormone, and insulin concentrations during various photoperiods in clinically normal horses and ponies and those with pituitary pars intermedia dysfunction

OBJECTIVE To measure plasma ACTH, alpha-melanocyte-stimulating hormone (aloha-MSH), and insulin concentrations during various photoperiods between February and October in horses and ponies with and without pituitary pars intermedia dysfunction (PPID). DESIGN Cohort study. ANIMALS 13 clinically normal (control) ponies, 14 clinically normal (control) horses, 7 ponies with PPID, and 8 horses with PPID. PROCEDURES Blood samples were collected from February through October during 8 photoperiods: 1, February 13 through March 2; 2, April 4 through 6; 3, June 19 through 22; 4, August 6 through 7; 5, August 14 through 17; 6, September 4 through 6; 7, September 26 through 28; and 8, October 16 through 18. Plasma ACTH, alpha-MSH, and insulin concentrations at each photoperiod were compared among groups. RESULTS Log ACTH concentration was increased during photoperiod 4 through 8, compared with photoperiod 1 through 3, in all groups. In photoperiod 3 through 7, log ACTH concentrations were higher in horses and ponies with PPID, compared with values for control horses and ponies. alpha-Melanocyte-stimulating hormone (log and raw value) concentration was higher in photoperiod 2 through 8, compared with photoperiod 1, in control horses and ponies. In horses and ponies with PPID, log alpha-MSH concentration was higher in photoperiod 3 through 8, and alpha-MSH concentration was higher in photoperiod 4 through 8, compared with photoperiod 1. In control horses and ponies, plasma insulin concentration was lower in photoperiod 3 than in photoperiod 1. CONCLUSIONS AND CLINICAL RELEVANCE Plasma alpha-MSH and ACTH concentrations increased as daylight decreased from summer solstice (maximum daylight hours) to 12 hours of daylight.

Neuroaxonal Dystrophy of the Accessory Cuneate Nucleus in Horses

Data were collected from 37 horses with a neurologic disability and compared to a group of 34 normal horses. Affected horses had neuroaxonal dystrophy, gliosis, vacuoles, and sometimes pigment localized to the accessory cuneate nuclei with minimal or no changes in the spinal cord and no changes in the proximal peripheral nerves. The focal nature of the change and usual absence of significant light microscopic spinal cord or peripheral nerve changes are different than previously described equine neuropathologic conditions.

Meningitis, cranial neuritis, and radiculoneuritis associated with Borrelia burgdorferi infection in a horse

CASE DESCRIPTION A 12-year-old Thoroughbred was examined because of signs of depression, neck stiffness, and poor performance. CLINICAL FINDINGS Physical examination revealed that the horse was dull, appeared depressed, was reluctant to raise its neck and head above a horizontal plane, and had a temperature of 38.5°C (101.3°F). No radiographic or scintigraphic abnormalities of the neck were found; however, high plasma fibrinogen concentration and relative lymphopenia were identified and the horse was seropositive for antibodies against Borrelia burgdorferi. Analysis of CSF revealed neutrophilic inflammation, and results of a PCR assay of CSF for B burgdorferi DNA were positive. Immunologic testing revealed severe B-cell lymphopenia and a low serum IgM concentration consistent with common variable immunodeficiency. TREATMENT AND OUTCOME The horse responded well to do×ycycline treatment (10 mg/kg [4.5 mg/lb], PO, q 12 h for 60 days) and returned to normal exercise. However, 60 days after treatment was discontinued, the horse again developed a stiff neck and rapidly progressive neurologic deficits, including severe ataxia and vestibular deficits. The horses condition deteriorated rapidly despite IV oxytetracycline treatment, and the horse was euthanatized. Postmortem examination revealed leptomeningitis, lymphohistiocytic leptomeningeal vasculitis, cranial neuritis, and peripheral radiculoneuritis with Wallerian degeneration; findings were consistent with a diagnosis of neuroborreliosis. CLINICAL RELEVANCE Nervous system infection with B burgdorferi should be considered in horses with evidence of meningitis and high or equivocal serum anti-B burgdorferi antibody titers. Evaluation of immune function is recommended in adult horses evaluated because of primary bacterial meningitis.

CAFFEINE CONTRACTURES, TWITCH CHARACTERISTICS AND THE THRESHOLD FOR CA2+-INDUCED CA2+ RELEASE IN SKELETAL MUSCLE FROM HORSES WITH CHRONIC INTERMITTENT RHABDOMYOLYSIS

Muscle from horses with intermittent exercise associated rhabdomyolysis was examined to determine if calcium regulation was abnormal. In vitro studies on semimembranosus muscle fibre bundles showed the time to 50 per cent relaxation of caffeine-induced contractures was shorter and the electrically elicited twitch longer in horses with exercise associated rhabdomyolysis. Substitution of strontium for calcium eliminated the difference in caffeine contracture between the normal and rhabdomyolysis horses. The threshold of calcium-induced calcium release was lower than normal in terminal cisternae-containing fractions of muscle from horses with rhabdomyolysis. Thoroughbreds with rhabdomyolysis had a shorter time to peak twitch tension than standardbreds, and normal thoroughbreds had a shorter caffeine contracture than normal standardbreds. There was no difference in fibre typing between breeds or groups. Either no histological changes or low grade to moderate degenerative myopathy was seen in muscle from horses with rhabdomyolysis. These results suggest horses with intermittent exercise associated rhabdomyolysis have abnormal calcium regulation.

Comparison of cortisol and ACTH responses after administration of thyrotropin releasing hormone in normal horses and those with pituitary pars intermedia dysfunction.

BACKGROUND Changes in both adrenocorticotropin (ACTH) and cortisol concentration in response to thyrotropin releasing hormone (TRH) administration have been used to diagnose equine pituitary pars intermedia dysfunction (PPID), but the use of the 2 hormones has not been compared. HYPOTHESES Measuring ACTH concentration is superior to measuring cortisol concentration after TRH administration in differentiating between normal horses and those with PPID, and the 2 hormone concentrations are disassociated in PPID horses. ANIMALS Eleven horses and 2 ponies with PPID and 19 normal horses. METHODS A study evaluating cortisol and ACTH concentrations before and at 14, 30, and 60 minutes after TRH administration. RESULTS At 14 and 30 minutes after TRH administration, cortisol concentration increased in PPID horses, and ACTH increased in all groups; ACTH, but not cortisol concentration, was significantly higher in PPID horses compared with normal horses. A relationship between cortisol concentration and ACTH concentration was seen in normal horses, but not in horses with PPID. Compared with normal castrated males, normal female horses had a greater change in cortisol concentration per unit change of ACTH concentration. CONCLUSIONS AND CLINICAL IMPORTANCE ACTH and cortisol concentrations are disassociated in horses with PPID. Measuring ACTH concentration after TRH administration appears superior to measuring cortisol concentration as a diagnostic test for PPID.

Chronic exertional rhabdomyolysis.

This article presents a brief description of what is known about the cause and pathogenesis of chronic intermittent rhabdomyolysis in horses. Clinically applicable diagnostic tests and published results in affected horses, prophylaxis, and treatment of the acute case are discussed.

Effects of cromolyn in horses with chronic obstructive pulmonary disease.

The effect of disodium cromoglycate (cromolyn) in preventing the pulmonary dysfunction caused by the inhalation of barn and hay dust was studied in 5 horses with confirmed chronic obstructive pulmonary disease (COPD). The horses were studied before (Con) and after exposure to hay and dust allergens (Expos) and after pretreatment with cromolyn followed by exposure (Cr-Expos).There was a significant reduction in PaO2 from 86.8±8.3 to 73.1±8.8 when the horses were exposed to hay and dust allergens. The PaO2 after pretreatment with cromolyn and exposures was 78.1±5.5. There were no significant changes in PaCO2, FRC, pH and A-aDO2 when the Con, Expos, and Cr-Expos periods were compared.There were significant increases in VE from a control value of 77.9±18.2 to 128.7±55.1 and 133.7±17.1 L/min during the exposures, which was due primarily to increases in respiratory frequency. Respiratory dead space (VD/VT) increased from 0.55±0.10 to 0.71±0.07 and 0.65±0.05, and alveolar ventilation (VE) remained constant. Pulmonary resistance (RL) and transpulmonary pressure (Ptr) increased from a control of 0.77±0.28 cm H2O/L/sec and 7.73±3.38 cm H2O to 2.93±1.01 and 20.17±4.81 during the Expos period and tidal volume (VT) fell from 7.5±1.0 to 5.7±1.3 L. The pre-treatment with cromolyn before exposures significantly reduced the increase in RL and Ptr and returned VT to Con levels.

Evaluation of Thyroid, Adrenal, and Pituitary Function

The clinical signs and endocrinologic abnormalities that characterize horses with pituitary, thyroid, and adrenal dysfunction are described. Laboratory tests and hormonal assays useful for evaluating horses with suspected endocrinopathies are discussed.