A comparison of idiopathic laryngeal paralysis in man and horse

Laryngeal paralysis: a study of 375 cases in a mixed-breed population of horses

Referred cases (n = 375) of laryngeal paralysis (1985-1998) from a mixed-breed equine population included 351 (94%) cases of recurrent laryngeal neuropathy (RLN) (idiopathic laryngeal hemiplegia) and 24 cases (6%) of laryngeal paralysis from causes other than RLN. Laryngeal movements were classified endoscopically into one of 6 grades, in contrast to the usual 4 grades. The RLN cases had a median grade 4 laryngeal paralysis, of which 96% were left-sided, 2% right-sided and 2% bilaterally affected. RLN cases included 204 (58%) Thoroughbred, 96 (27%) Thoroughbred-cross, 23 (7%) draught, 16 (5%) Warmbloods and 10 (3%) other breeds, including only 4 (1%) ponies. The median age of RLN cases at referral was 6 years (range 2-12) and their median height was 170.2 cm. The work of RLN horses included National Hunt racing (42%), flat racing (1%), hunting (19%), eventing (16%) and miscellaneous work (22%). Reported presenting signs in RLN-affected horses included abnormal exercise-related respiratory sounds in 90% and reduced exercise tolerance in only 64%. However, many horses were referred before their exercise tolerance could be fully assessed. Forty percent of the RLN cases had intercurrent disorders, including 10% with additional upper respiratory and 7% with lower respiratory tract diseases. The 24 nonidiopathic RLN cases included 12 with bilateral laryngeal paralysis, 11 (92%) of which were ponies. Bilateral laryngeal paralysis occurred with hepatic encephalopathy in 7 cases and following general anaesthesia in 2 cases. The 12 cases of acquired unilateral laryngeal paralysis included 7 caused by guttural pouch mycosis.

Career racing performance in Thoroughbreds treated with prosthetic laryngoplasty for laryngeal neuropathy: 52 cases (1981-1989)

OBJECTIVE

To compare racing performance before and after prosthetic laryngoplasty for treatment of laryngeal neuropathy in inexperienced and experienced Thoroughbred racehorses.

DESIGN

Retrospective study.

ANIMALS

52 Thoroughbred racehorses treated with prosthetic laryngoplasty for laryngeal neuropathy.

PROCEDURE

Lifetime race records were analyzed by use of a verified regression model. Individual race records and hospital records were also reviewed.

RESULTS

Experienced horses had a decline in performance, as measured by performance index, earnings percentage, and mean prediction error, during the 6-month period before prosthetic laryngoplasty. Performance improved after surgery, relative to performance in 1 to 4 races immediately before surgery, but did not attain previous baseline values for performance index and earnings percentage, although racing speed was restored to baseline values. Factors associated with failure to attain baseline levels of performance included other racing-related injuries and disorders, major complications of surgery, and age. Individually, however, many horses had long and successful careers after surgery. Performance of inexperienced horses after surgery was at least equal to that of experienced horses.

CONCLUSIONS AND CLINICAL RELEVANCE

In addition to warning clients of the complications associated with prosthetic laryngoplasty, it may be prudent to provide a guarded prognosis for full restoration of racing performance in older horses, unless they are especially talented and are free of other racing-related problems.

Poor performance and field evaluation of the respiratory system

A thorough examination of the respiratory system is an important part of the work-up for poor performance in horses. This article provides a systematic approach to field evaluation of horses with poor performance due to respiratory system dysfunction. The information is organized to help the reader evaluate pertinent historical and physical examination findings so that a list of differential diagnoses can be generated. Also, pertinent ancillary diagnostic modalities that can help further characterize and localize causes for respiratory dysfunction in horses presented for poor performance are discussed.

Blood gas tensions, acid-base status, heart rates, and venous profiles in exercising horses with laryngeal hemiplegia before and after corrective surgery

The physiologic effects of exercise were studied in four horses with complete laryngeal hemiplegia. Right carotid arteries were surgically elevated to a subcutaneous position for percutaneous catheterization. Each horse was fitted with a device designed to obtain multiple arterial samples while the horse was exercised over a 1.6-km course. After each horse completed 10 test gallops, the laryngeal hemiplegia was treated using a laryngeal prothesis and ventriculectomy. The horses were then reconditioned, and the exercise test and sampling were repeated. Horses with laryngeal hemiplegia became acidotic, hypoxic, and hypercapnic compared to normal horses. Surgical treatment improved blood gas and acid-base status, but the values were not equivalent to those in normal horses similarly tested.

Determination of the early age of onset of equine recurrent laryngeal neuropathy. 1. Muscle pathology

The age of onset of equine recurrent laryngeal neuropathy has not been ascertained, although the clinical condition of left laryngeal hemiplegia ("roaring") has been recognized for centuries. The purpose of this study was to evaluate the laryngeal muscles of draft horse foals for the presence of fiber-type grouping, indicating denervation and reinnervation, and to determine if histological evidence of recurrent laryngeal neuropathy was present. Abductor and adductor laryngeal muscles from the left and right sides were collected immediately after euthanasia from male draft horse foals, six less than 2 weeks and four 6 months of age, and stained for myosin ATPase. A morphometric test was used to objectively evaluate several areas from each muscle for fiber-type grouping. Extensive fiber-type grouping which was characteristic of recurrent laryngeal neuropathy was found in one of the young foals and all of the older foals. Four of the young foals had some areas of fiber-type grouping suggestive of mild, early changes associated with recurrent laryngeal neuropathy. One of the young foals had no fiber-type grouping present in any of the laryngeal muscles evaluated. These findings suggest an early age of onset of recurrent laryngeal neuropathy.

Upper airway function during maximal exercise in horses with obstructive upper airway lesions. Effect of surgical treatment

Upper airway pressure was measured during maximal exercise in 10 Thoroughbred racehorses with naturally occurring upper airway obstruction. Left laryngeal hemiplegia and arytenoid chondropathy resulted in substantial increases (30-40 cm H2O) in inspiratory upper airway pressure (Pl), whereas complicated aryepiglottic entrapment and subepiglottic cysts produced only modest increases (15 cm H2O) in Pl. Uncomplicated aryepiglottic entrapment and grade IV pharyngeal lymphoid hyperplasia produced only slight increases (3-5 cm H2O). In general, surgical procedures restored airway pressures to within normal limits. Subtotal arytenoidectomy improved but did not normalize airway pressures in horses with arytenoid chondropathy. Pharyngeal lymphoid hyperplasia appeared to have little effect on upper airway function.

Effects of left recurrent laryngeal neurectomy, prosthetic laryngoplasty, and subtotal arytenoidectomy on upper airway pressure during maximal exertion

Upper airway pressure was measured with a nasotracheal catheter system and a portable pressure transducer in 10 normal horses during maximal exercise before and after left recurrent laryngeal neurectomy. Measurements were repeated 16 weeks after prosthetic laryngoplasty (5 horses) or subtotal arytenoidectomy (5 horses). During maximal exertion, prosthetic laryngoplasty was more effective than subtotal arytenoidectomy in reversing the increases in upper airway pressure that followed left recurrent laryngeal neurectomy.

Vocal cord paralysis following carotid endarterectomy: the paradox of return of function

In a series of 411 consecutive carotid endarterectomies 29 patients were identified with vocal cord paralysis. All patients were symptomatic, although in many these symptoms were subtle and rapidly resolved. There was a statistically significant predominance of left-sided paralysis. Excluding three patients who died during the initial year of follow-up return of normal voice was noted in 22 patients, but complete return of vocal cord function was present in only 15. Apposition of the contralateral vocal cord against a paralyzed vocal cord allowed for production of normal voice in five patients. Less than 1% of patients remained with symptoms at one year following endarterectomy. We conclude that vocal cord paralysis is a common complication of carotid endarterectomy; the voice becomes an unreliable guide as to its resolution. We recommend laryngoscopic examination of all patients who undergo bilateral carotid endarterectomy.

The pathogenesis of equine laryngeal hemiplegia — a review

Recent research on the muscular and nervous changes which occur in idiopathic equine laryngeal hemiplegia has indicated that many of the traditional concepts of the aetiology of this disease are erroneous. In light of the new knowledge gained, the various predispositions and possible causes of laryngeal hemiplegia are discussed, and it is suggested that the underlying mechanism of axonal damage in this neuropathy of horses may be related to abnormal energy metabolism in the axon.

Recurrent laryngeal nerve paralysis. A 10-year review of 564 patients

A retrospective review of the clinical records of 564 patients with recurrent laryngeal nerve paralysis examined at the Department of Otolaryngology, Kurume University Hospital during the 10-year period from 1971 to 1980 was completed. The results are summarized as follows: 1) Two-hundred and ninety-three patients were male and 271, female. The incidence was high in old age groups. 2) Idiopathic paralysis (233 cases) was the most frequent and paralysis caused by thyroid surgery (68 cases) and endotracheal intubation (63 cases) came next. 3) The lesion was unilateral in 519 patients (right to left = 148 to 371) and bilateral in 45. 4) The paralytic vocal fold was fixed in the paramedian position in the majority of the patients. A limited movement of the paralytic fold was observed in some cases, especially those of paralysis caused by endotracheal intubation and idiopathic paralysis. 5) A compensatory overcrossing of the unaffected vocal fold was found in 41 patients. It developed within six months from the onset in most cases. 6) Spontaneous recovery and improvement of mobility took place in 54 of the 165 patients who could be followed up for 1 year or longer. Paralysis caused by endotracheal intubation showed the best prognosis and idiopathic paralysis came next. 7) Spontaneous voice recovery and improvement occurred in 183 of the 240 patients whose voice outcome was determined. 8) Phonosurgical treatments yielded good results in most cases. Some patients, however, had their voice receded later.

Measurement of specific laryngeal muscle function by ultrasound

Ultrasonic dimension gauges were implanted in the crico-arytenoideus dorsalis muscle in a mature horse. Resting and contracted muscle length and average contraction rate were measured serially in the conscious state over a period of 25 days. Results suggest that specific laryngeal muscle function in the horse may be defined with this approach. Since man and horse are both known to suffer from laryngeal hemiplegia, this experimental preparation may help provide information of benefit to both species.

A correlation of the endoscopic and pathological changes in subclinical pathology of the horse's larynx

The larynges of 6 horses were examined endoscopically and the findings correlated with the gross and histological appearance of the intrinsic laryngeal muscles and their nerve supply. In all cases it appeared that the balance between abductor and adductor muscle groups had been lost due to preferential atrophy of individual muscles or groups of muscles. The laryngeal abnormalities recorded were asymmetry of the larynx with asynchronous left sided abduction and fluttering or trembling of the left vocal cord and arytenoid cartilage. It is suggested that these changes represent the early signs of a progressive lesion which may result in left sided laryngeal hemiplegia.