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 horse's 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.
Objective—To evaluate risk factors associated with
development of catheter-associated jugular thrombophlebitis
in hospitalized horses.
Design—Retrospective case-control study.
Animals—50 horses with thrombophlebitis and 100
Procedure—Medical records from 1993 through 1998
were searched for horses with thrombophlebitis.
Horses that were hospitalized for at least 5 days, had an
IV catheter placed in a jugular vein (other than for solely
anesthetic purposes), and had no evidence of thrombophlebitis
during admission or hospitalization were
chosen as controls. Signalment, history, clinicopathologic
findings, primary illness, and treatment were
obtained from the medical records. Data were analyzed
by use of logistic regression to perform univariate and
Results—For a horse with endotoxemia, the odds of
developing thrombophlebitis were 18 times those for a
similar horse without endotoxemia. For a horse with salmonellosis,
the odds of developing thrombophlebitis
were 68 times those for a similar horse without salmonellosis.
For a horse with hypoproteinemia, the odds of
developing thrombophlebitis were almost 5 times those
for a similar horse without hypoproteinemia. For a horse
in the medicine section, the odds of developing thrombophlebitis
were 16 times those for a similar horse in
the surgery section. For a horse with large intestinal disease,
the odds of developing thrombophlebitis were 4
times those for a similar horse without large intestinal
disease. For a horse receiving antidiarrheal or antiulcerative
medications, the odds of developing thrombophlebitis
were 31 times those for a similar horse not
receiving these medications.
Conclusions and Clinical Relevance—Results indicated
that patient factors, including large intestinal disease,
hypoproteinemia, salmonellosis, and endotoxemia,
were associated with development of catheter-associated
thrombophlebitis in horses. (J Am Vet Med Assoc 2005;227:1134–1141)
Objective—To measure plasma ACTH, D-melanocyte–stimulating hormone (D-MSH), and insulin concentrations during various photoperiods between February and October in horses and ponies with and without pituitary pars intermedia dysfunction (PPID).
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, D-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. D-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 D-MSH concentration was higher in photoperiod 3 through 8, and D-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 D-MSH and ACTH concentrations increased as daylight decreased from summer solstice (maximum daylight hours) to 12 hours of daylight.
Objective—To compare the effect of thyrotropin-releasing hormone (TRH) administration on endogenous ACTH concentrations in healthy horses and those with pituitary pars inter-media hyperplasia and compare the test with the dexamethasone suppression test (DST).
Design—Prospective case series.
Animals—15 horses with clinical signs of pituitary pars intermedia dysfunction (PPID), 4 horses with equivocal signs of PPID, and 29 horses without signs of PPID.
Procedures—ACTH concentrations prior to and after administration of TRH were measured 61 times in 48 horses. Results of the DST (cortisol response) were compared with those of the TRH test in 29 horses. Thirty-three horses (24 with no clinical signs of PPID, 5 with clinical signs of PPID, and 4 with equivocal clinical signs of PPID) were euthanized and necropsied and their pituitary glands evaluated.
Results—ACTH concentrations increased in all horses, but magnitude and duration of increase were significantly higher in horses with PPID. Endogenous ACTH concentrations were influenced by season. The ACTH baseline concentrations and response to TRH were not correlated with results of the DST. Results of DST were abnormal only in clinically abnormal horses or those with pars intermedia hyperplasia, but were within reference range in 17 of 26 tests in these horses.
Conclusions and Clinical Relevance—The ACTH response to TRH is a useful test for diagnosis of pituitary gland hyperplasia, particularly in horses in which baseline ACTH concentrations are within reference range. The DST was specific but not sensitive and was inconsistent for individuals, and results often did not agree with the TRH test response.
Objective—To determine sensitivity of equine skeletal
muscle to tetrodotoxin and compare that with sensitivity
of murine and human skeletal muscles.
Sample Population—Semimembranosus, vastus lateralis,
triceps brachii, and masseter muscle specimens
from 22 euthanatized horses, vastus lateralis
muscle biopsy specimens from 25 clinically normal
humans, and diaphragmatic muscle specimens from
Procedure—Electrically elicited twitch responses
were measured in muscle specimens incubated in
medium alone and with tetrodotoxin (100 nM, 400
nM, 1.6 µM for equine specimens and 100 nM, 200
nM, 400 nM, 800 nM, 1.6 µM for murine and human
specimens). Percentages of tetrodotoxin-sensitive
and -resistant sodium channels were determined and
compared among muscles and species.
Results—2 sodium channels with different sensitivities
to tetrodotoxin were identified in equine muscle.
One was blocked with 100 nM tetrodotoxin and the
other was unaffected by tetrodotoxin at concentrations
up to 1.6 µM. The only difference detected
among the 4 equine muscles was that masseter muscle
specimens had a higher percentage of tetrodotoxin-
sensitive channels than triceps brachii muscle
specimens. Tetrodotoxin-resistant sodium channels
constituted 31 to 66% of the equine muscle twitch
response, which was greater than that determined
for normal human and murine muscle (< 5%).
Conclusion and Clinical Relevance—Equine skeletal
muscle contains a high percentage of tetrodotoxin-resistant sodium channels. The 4 equine muscles
evaluated were more similar to each other than to
murine and human muscles. Shifts in expression of
sodium channel subtypes may play a role in the manifestation
of certain myopathies. (Am J Vet Res
Objective—To determine prevalence and clinical features
of pituitary pars intermedia dysfunction (PPID)
in horses with laminitis.
Animals—40 horses with laminitis.
Procedures—Horses with laminitis that survived an
initial episode of pain and were not receiving medications
known to alter the hypothalamic-pituitary-adrenal
axis were tested for PPID by evaluation of endogenous
plasma ACTH concentration. Signalment, suspected
cause, month of onset and duration of laminitis,
Obel grade of lameness, pedal bone rotation,
physical examination findings, results of endocrine
function tests, treatment, outcome, and postmortem
examination findings were recorded.
Results—Prevalence of PPID as defined by a single
high plasma ACTH concentration was 70%. Median
age of horses suspected of having PPID (n = 28) was
15.5 years, and median age of horses without PPID
(12) was 14.5 years. Laminitis occurred most frequently
in horses with and without suspected PPID
during September and May, respectively. Chronic
laminitis was significantly more common in horses
suspected of having PPID. In horses suspected of having
PPID, the most common physical examination findings
included abnormal body fat distribution, bulging
supraorbital fossae, and hirsutism. Five horses suspected
of having PPID had no clinical abnormalities
other than laminitis. Seventeen horses suspected of
having PPID that were treated with pergolide survived,
and 3 horses that were not treated survived.
Conclusions and Clinical Relevance—Evidence of
PPID is common among horses with laminitis in a primary-care ambulatory setting. Horses with laminitis
may have PPID without other clinical signs commonly
associated with the disease. (J Am Vet Med Assoc
Objective—To evaluate the correlation between plasma
α-melanocyte-stimulating hormone (α-MSH) concentration
and body mass index (BMI) in healthy horses.
Animals—82 healthy horses.
Procedure—Plasma α-MSH concentration was determined
by radioimmunoassay. At the time blood samples
were collected, body condition scores (BCS)
were determined and measurements of girth circumference,
body length, and height were obtained.
Weight was estimated by use of the following
formula: estimated weight (kg) = [girth (cm)2 × length
(cm)]/11,877. Body mass index was calculated as estimated
weight (kg)/height (m)2.
Results—A correlation was found between BMI and
BCS (rs = 0.60 [95% confidence interval (CI), 0.44 to
0.73]). A weak correlation was found between plasma
α-MSH concentration and BMI (rs = 0.25 [95% CI,
0.03 to 0.45]) and BCS (rs = 0.26 [95% CI, 0.04 to
0.46]). A correlation was found between plasma
α-MSH concentration and BMI in horses ≥ 10 years
old (rs = 0.49 [95% CI, 0.20 to 0.69]) but not in horses
< 10 years old (rs = –0.04). Horses in the upper
quartile of BMI had significantly greater plasma α-MSH concentration (median, 9.1 pmol/L; range, 2.0 to
95.3 pmol/L) than horses in the lowest quartile of BMI
(median, 7.0 pmol/L; range, 3.6 to 15.7 pmol/L).
Conclusions and Clinical Relevance—A correlation
exists between plasma α-MSH concentration and
BMI in horses. Further study is required to determine
whether melanocortin receptor defects underlie this
correlation or, alternately, whether plasma α-MSH
concentration is simply a correlate of adiposity. (Am J Vet Res 2004;65:1469–1473)
Objective—To determine effects of age and pituitary pars intermedia dysfunction (PPID) on corneal sensitivity in horses.
Animals—20 adult horses allocated into 3 groups (PPID group, old [> 15 years old] horses with PPID [n = 5]; old group, old [> 15 years old] horses without PPID ; and young group, young [≤ 10 years old] horses without PPID ). All horses with PPID had hirsutism and abnormal fat deposition or laminitis; none of the old or young horses had hirsutism, abnormal fat deposition, or laminitis.
Procedures—A Cochet-Bonnet aesthesiometer was used to measure the corneal touch threshold (CTT) in both eyes of each horse. The nylon monofilament was applied at a maximum length of 60 mm to the central region of the cornea and length was decreased by 5-mm increments until a consistent blink response was elicited. Tear production was assessed in all eyes via the Shirmer tear test (STT).
Results—Mean ± SD CTT was significantly greater for young horses (47.50 ± 4.52 mm) than for horses in the old (28.06 ± 5.72 mm) and PPID (21.5 ± 3.37 mm) groups. Old horses had significantly higher CTT values than did horses with PPID. The STT values were within the reference range for all groups and did not differ significantly among groups.
Conclusions and Clinical Relevance—Corneal sensitivity decreased with both age and PPID. Because decreased corneal sensitivity is associated with impaired wound healing, increasing age and PPID may increase the risk for nonhealing or recurrent corneal ulcers in horses.
Case Description—A 6-month-old male Bactrian camel was examined because of a 3-week history of lameness of the left hind limb.
Clinical Findings—Lameness was initially detected in the left hind limb but resolved and was detected in the right hind limb during treatment. Lameness increased during periods of rapid growth. Radiography revealed multiple small opacities of the medullary cavity of several long bones throughout treatment. Core bone biopsies of lesions in the tibiae revealed lamellar bone with areas of loose connective tissue, osteoblasts in the medullary cavity, and periosteal new bone formation, all which were consistent with panosteitis.
Treatment and Outcome—Palliative treatment was attempted with epidural and transdermal administration of analgesics. Flunixin meglumine was administered PO, which coincided with an abrupt increase in serum creatinine concentration. Performance of multiple diagnostic bone biopsies led to remission of clinical signs of pain.
Clinical Relevance—Panosteitis should be a differential diagnosis for shifting limb lameness in young camels. Bone biopsies can be useful for diagnosis of panosteitis and possible relief of pain associated with the disease. Bactrian camels may be susceptible to the renal toxicity of flunixin meglumine, especially when dehydrated.
Objective—To compare endogenous ACTH and α-melanocyte-stimulating hormone (α-MSH) concentrations after administration of thyrotropin-releasing hormone (TRH) and to compare ACTH concentrations after TRH administration with those following domperidone administration in healthy horses and horses with pituitary pars intermedia dysfunction (PPID).
Design—Prospective case series.
Animals—69 clinically normal horses and 47 horses with or suspected to have PPID.
Procedures—ACTH concentrations were measured during 108 TRH stimulation tests in 88 horses, and α-MSH concentrations were measured during 56 TRH stimulation tests in 50 horses. In 28 of these horses, ACTH concentrations after domperidone administration were measured and test results were compared. The pituitary gland was histologically examined in all horses that were euthanatized.
Results—ACTH and α-MSH concentrations increased in all horses afterTRH administration, with a greater and more prolonged increase in horses with PPID. Percentage increase was significantly greater for α-MSH concentration than for ACTH concentration. The change in ACTH concentration after domperidone administration was less consistent in differentiating clinically normal horses from those with PPID than was the response to TRH.
Conclusions and Clinical Relevance—Results suggested that ACTH concentration in response to TRH administration was useful for the diagnosis of PPID in horses and appeared more accurate than response to domperidone administration. Use of an α-MSH concentration ≥ 30 or 50 pmol/L did not appear superior to use of an ACTH concentration ≥ 36 pg/mL for the diagnosis of PPID, either before or 30 minutes after TRH administration.