Effect of deoxycorticosterone acetate-salt-induced hypertension on diabetic peripheral neuropathy in alloxan-induced diabetic WBN/Kob rats

The relationship between hypertension and diabetic peripheral neuropathy (DPN) has recently been reported in clinical research, but it remains unclear whether hypertension is a risk factor for DPN. To investigate the effects of hypertension on DPN, we analyzed morphological features of peripheral nerves in diabetic rats with hypertension. Male WBN/Kob rats were divided into 2 groups: alloxan-induced diabetic rats with deoxycorticosterone acetate-salt (DOCA-salt) treatment (ADN group) and nondiabetic rats with DOCA-salt treatment (DN group). Sciatic, tibial (motor) and sural (sensory) nerves were subjected to qualitative and quantitative histomorphological analysis. Systolic blood pressure in the two groups exhibited a higher value (>140 mmHg), but there was no significant difference between the two groups. Endoneurial blood vessels in both groups presented endothelial hypertrophy and narrowing of the vascular lumen. Electron microscopically, duplication of basal lamina surrounding the endothelium and pericyte of the endoneurial vessels was observed, and this lesion appeared to be more frequent and severe in the ADN group than the DN group. Many nerve fibers of the ADN and DN groups showed an almost normal appearance, whereas morphometrical analysis of the tibial nerve showed a significant shift to smaller fiber and myelin sizes in the ADN group compared with DN group. In sural nerve, the fiber and axon-size significantly shifted to a smaller size in ADN group compared with the DN group. These results suggest that combined diabetes and hypertension could induce mild peripheral nerve lesions with vascular changes.     

Temporary right recurrent laryngeal neuropathy in a horse associated with a left prosthetic laryngoplasty procedure

Right recurrent laryngeal neuropathy (RLN) is an uncommon, acquired disease for which the aetiology can frequently be diagnosed. Numerous aetiologies have been proposed for right‐sided RLN which comprises 2% of all cases of RLN. In this report we discuss the clinical course, treatment and outcome following right‐sided laryngeal paralysis as a complication of left‐sided prosthetic laryngoplasty in a horse. To the authors' knowledge, this is the first report of such a surgical complication.     

Pyridoxine induced neuropathy by subcutaneous administration in dogs

To construct a sensory neuropathy model, excess pyridoxine (150 mg/kg s.i.d.) was injected subcutaneously in dogs over a period of 7 days. During the administrations period, the dogs experienced body weight reduction and proprioceptive loss involving the hindquarters. After pyridoxine administration was completed, electrophysiological recordings showed that the M wave remained at a normal state, but the H-reflex of the treated dogs disappeared at 7 days. The dorsal funiculus of L₄ was disrupted irregularly in the axons and myelin with vacuolation. The dorsal root ganglia of L₄, and sciatic and tibial nerves showed degenerative changes and vacuolation. However, the lateral and ventral funiculi of L₄ showed a normal histopathologic pattern. Although this subcutaneous administration method did not cause systemic toxicity and effectively induced sensory neuropathy, this study confirmed the possibility of producing a pyridoxine-induced sensory neuropathy model in dogs with short-term administration.     

Resistance of the Peripheral Nervous System to the Effects of Chronic Canine Hypothyroidism

Background: Hypothyroidism has been implicated in the development of multiple peripheral mono‐ and polyneuropathies in dogs. The objectives of this study were to evaluate the clinical and electrophysiologic effects of experimentally induced hypothyroidism on the peripheral nervous system of dogs. Hypothesis: Chronic hypothyroidism will induce peripheral nerve sensorimotor dysfunction. Animals: Eighteen purpose‐bred, female dogs. Methods: Prospective, longitudinal study: Hypothyroidism was induced by radioactive iodine administration in 9 dogs, and the remaining 9 served as untreated controls. Neurological examinations were performed monthly. Electrophysiologic testing consisting of electromyography (EMG); motor nerve conduction studies of the sciatic‐tibial, radial, ulnar, and recurrent laryngeal nerves; sciatic‐tibial and ulnar F‐wave studies; sensory nerve conduction studies of the tibial, ulnar, and radial nerves; and evaluation of blink reflex and facial responses were performed before and 6, 12, and 18 months after induction of hypothyroidism and compared with controls. Results: Clinical evidence of peripheral nervous dysfunction did not occur in any dog. At 6 month and subsequent evaluations, all hypothyroid dogs had EMG and histologic evidence of hypothyroid myopathy. Hypothyroid dogs had significant (P≤ .04) decreases in ulnar and sciatic‐tibial compound muscle action potentials over time, which were attributed to the concurrent myopathy. No significant differences between control and hypothyroid dogs were detected in electrophysiologic tests of motor (P≥ .1) or sensory nerve conduction velocity (P≥ .24) or nerve roots (P≥ .16) throughout the study period, with values remaining within reference ranges in all dogs. Conclusion: Chronic hypothyroidism induced by thyroid irradiation does not result in clinical or electrophysiologic evidence of peripheral neuropathy, but does cause subclinical myopathy.     

ULTRASONOGRAPHY OF PERIPHERAL NERVES IN THE NORMAL ADULT HORSE

A study of the ultrasonographic appearance and size of the sciatic, tibial, peroneal, suprascapular, radial, median, and ulnar nerves and a comparison with the anatomic size and location of these nerves in the normal adult horse is reported. Cadavers and live horses were studied. Landmarks for localization and techniques for nerve identification are described. The depth and diameter of each nerve at various locations and the success rate in imaging each nerve are reported. Statistically significant correlations were found between anatomically and ultrasonographically measured nerve depths and diameters. The success rate in identifying nerves was 70% in the live horses and 49% in cadavers, with the deep peroneal nerve being the easiest to identify. Some applications of this technique in horses are discussed.     

Histological and ultrastructural evidence that recurrent laryngeal neuropathy is a bilateral mononeuropathy limited to recurrent laryngeal nerves

Reasons for performing study: Recurrent laryngeal neuropathy (RLN) is a common and debilitating peripheral nerve disease of horses, but it remains unclear if this disease is a mono‐ or polyneuropathy. An understanding of the distribution of the neuropathological lesions in RLN affected horses is fundamental to studying the aetiology of this very significant disease of tall horses. Objective: To determine whether RLN should be classified as a mono‐ or polyneuropathy. Methods: Multiple long peripheral nerves and their innervated muscles were examined systematically in 3 clinically affected RLN horses Results: Severe lesions were evident in the left as well as right recurrent laryngeal nerves in all horses, both distally and, in one case, also proximally. No primary axonal lesions were evident in other nerves nor were changes found in their innervated muscles. Conclusions: RLN is not a polyneuropathy but should be classified as a bilateral mononeuropathy. Potential relevance: Genetic and local factors specifically affecting the recurrent laryngeal nerves in RLN‐affected horses should now be investigated further.     

Fifty years of recurring struggles with recurrent laryngeal neuropathy

Recurrent laryngeal neuropathy appears to be a simple problem that should have a simple solution, yet the complexity and dynamic nature of laryngeal function is underappreciated. This review highlights the challenges and accomplishments that work towards that greater understanding of what is necessary to find a successful solution.     

Caudal compression of the infraorbital nerve: A novel surgical technique for treatment of idiopathic headshaking and assessment of its efficacy in 24 horses

Reasons for designing and reporting technique: Idiopathic headshaking has remarkable similarities to human neuropathic facial pain syndromes associated with post herpetic and trigeminal neuralgia. These derive from abnormal sensory function within the peripheral or central pathways of the trigeminal nerve (TgN). Limiting input from the TgN can be helpful in controlling the perception of pain. Rhizotomy of the infraorbital branch of the TgN as it emerges from the infraorbital canal has been reported but has a poor efficacy. A novel technique involves compression of the nerve at a more caudal location within the infraorbital canal and the technique requires validation. Hypothesis: Caudal compression of the infraorbital nerve with platinum coils, performed in horses diagnosed with idiopathic headshaking, results in a decrease in clinical signs. Methods: Caudal compression of the infraorbital nerve, using platinum embolisation coils, was performed under fluoroscopic guidance. Clinical records of 24 idiopathic headshakers that had undergone this procedure were reviewed. Follow‐up information was obtained by telephone questionnaire with the owner or referring veterinary surgeon. Results: All 24 horses had at least one surgical procedure. Median follow‐up time was 6 months. There were 2 horses which had surgery 2 weeks before follow‐up and these were excluded from the analysis of outcome. Following one surgery, 13/22 horses (59.0%) had a successful outcome. Of the 9 horses that did not improve, surgery was repeated in 6 cases. Two of these horses had a successful outcome. Overall, a successful outcome was obtained in 16/19 horses (84.2%). Conclusions: This surgical technique is likely to prevent input from the TgN at a more caudal location then the previously described infraorbital neurectomy. The technique requires refinement.     

Correlation of the Havemeyer endoscopic laryngeal grading system with histopathological changes in equine Cricoarytenoideus dorsalismuscles

The establishment of a single validated endoscopic laryngeal grading system for assessing recurrent laryngeal neuropathy (RLN) is desirable to facilitate direct comparisons between the findings of different clinical and research groups worldwide. The objective of this study was to assess the relationship between the Havemeyer endoscopic laryngeal grading system and histopathological changes consistent with RLN in the left cricoarytenoideus dorsalis (CAD) muscle of horses of different breeds with a full range of clinical severities of RLN, i.e., from normal endoscopic laryngeal function to complete laryngeal hemiplegia. Endoscopic grading of laryngeal function of 22 horses was performed using the Havemeyer endoscopic laryngeal grading system. A biopsy sample of the left CAD muscle was obtained from each horse, either at post mortem examination (n = 16), or during routine laryngoplasty surgery (n = 6). A semi-quantitative histopathological scoring system was used to grade the severity of histopathological lesions consistent with RLN in the left CAD muscle of each horse. A significant positive correlation (rs = 0.705, p < 0.001) was found between the Havemeyer grades and sub-grades of laryngeal function and the semi-quantitative assessment of histopathological lesions consistent with RLN in the left CAD muscle. However, a wide spread of muscle histopathological scores was obtained, particularly from horses with Havemeyer sub-grades II.1, III.1 and III.2. In conclusion, the Havemeyer endoscopic laryngeal grading system was found to broadly correlate with histopathological changes consistent with RLN in equine cricoarytenoideus dorsalis muscle.     

DIAGNOSTIC SENSITIVITY OF SUBJECTIVE AND QUANTITATIVE LARYNGEAL ULTRASONOGRAPHY FOR RECURRENT LARYNGEAL NEUROPATHY IN HORSES

Recurrent laryngeal neuropathy (RLN) is the most common cause of laryngeal hemiplegia in horses and causes neurogenic atrophy of the intrinsic laryngeal muscles, including the cricoarytenoideus lateralis muscle. Recurrent laryngeal neuropathy results in paresis to paralysis of the vocal fold and arytenoid cartilage, which limits performance through respiratory compromise. Ultrasound has previously been reported to be a useful diagnostic technique in horses with RLN. In this report, the diagnostic sensitivity of subjective and quantitative laryngeal ultrasonography was evaluated in 154 horses presented for poor performance due to suspected upper airway disease. Ultrasonographic parameters recorded were: cricoarytenoideus lateralis echogenicity (subjective and quantitative), cricoarytenoideus lateralis thickness, vocal fold movement, and arytenoid cartilage movement. Ultrasonographic parameters were then compared with laryngeal grades based on resting and exercising upper airway endoscopy. Subjectively increased left cricoarytenoideus lateralis echogenicity yielded a sensitivity of 94.59% and specificity of 94.54% for detecting RLN, based on the reference standard of exercising laryngeal endoscopy. Quantitative left cricoarytenoideus lateralis echogenicity values differed among resting laryngeal grades I–IV. Findings from this study support previously published findings and the utility of subjective and quantitative laryngeal ultrasound as diagnostic tools for horses with poor performance.     

Progressive myelopathy and neuropathy in New Zealand Huntaway dogs

Aim: To investigate the nature and cause of a progressive ataxia in three 20-month-old Huntaway dogs that were litter mates.

Methods: Affected dogs were examined before they were humanely killed and submitted to necropsy. Selected formalin-fixed tissues were examined by light and electron microscopy.

Results: The lesions were those of axon and myelin degeneration within sensory, proprioceptive and motor tracts of the spinal cord and to a lesser degree some peripheral nerves.

Conclusion: A progressive myelopathy and neuropathy, tentatively described as a central-peripheral distal axonopathy, was present in all 3 dogs.The cause was not determined but was likely to be either genetic or nutritional.

Clinical relevance: In the early stages of this disease, careful examination maybe necessary to distinguish the signs of ataxia from orthopaedic disease such as hip dysplasia. Affected animals are unlikely to be of use as working dogs.     

Pasture-associated stringhalt: Contemporary appraisal of an enigmatic syndrome

Although described clinically for several centuries, stringhalt remains an intriguing and enigmatic condition. In pasture-associated stringhalt (PSH), the clinical sign of exaggerated, prolonged hindlimb flexion is associated with a peripheral neuropathy affecting the larger myelinated axons that is thought to be the result of exposure to a plant-derived neurotoxin. It is likely that multiple host and environmental risk factors interact to produce PSH and the precise aetiology has not yet been elucidated. Drought-affected, poor-quality pasture and the presence of Hypochoeris radicata (commonly referred to as Catsear, Flatweed and False Dandelion) are recognised risk factors. Affected horses are typically mature and taller animals are considered more susceptible. Most horses with PSH recover spontaneously if removed from the presumptive source of toxin; however, recovery can be prolonged, taking several years for some horses, and might be incomplete in occasional cases. A wide range of therapies have been attempted in horses with PSH including phenytoin, thiamine, taurine, infiltration of digital extensors with botulinum toxin and lateral digital extensor myotenectomy procedure. The efficacy of these treatments is uncertain since controlled trials have not been performed and the spontaneous recovery of most horses makes any response to treatment difficult to interpret.     

A neurologic syndrome in Golden Retrievers presenting as a sensory ataxic neuropathy

BACKGROUND: A sensory ataxic neuropathy has been observed in Swedish Golden Retrievers recently. ANIMALS: Twenty-one affected Golden Retrievers. METHODS: Clinical and neurologic status, electrophysiologic, and pathologic status as well as pedigree analyses were evaluated. RESULTS: Clinical signs had an insidious onset between 2 and 8 months of age and a slowly progressive course. Affected dogs were ataxic and dysmetric. They had abnormal postural reactions and decreased spinal reflexes but no apparent muscle atrophy. Clinical pathology, radiography, and electrophysiology of motor systems were all within reference values. Sensory nerve conduction results of affected dogs were significantly different from those of a group of control dogs. Necropsy revealed a chronic progressive central and peripheral sensorimotor axonopathy; the proprioceptive pathways were most severely affected. CONCLUSIONS AND CLINICAL IMPORTANCE: This disease in these Golden Retrievers is distinct from other canine breed-related neurodegenerative diseases or hereditary neurodegenerative diseases described in humans. Pedigree analyses indicated a hereditary background, but the mode of inheritance could not be established.     

Retinal and optic nerve degeneration in cattle after accidental acrylamide intoxication

A herd of cattle was accidentally exposed to monomeric acrylamide and N-methylolacrylamide. Seven cattle underwent repeated examinations during 6–8 months after exposure. Abnormal pupillary light reflexes (PLR) were observed in one cow. Ophthalmoscopic examination showed progressive retinal degeneration and degenerative changes in the optic nerve heads in this cow. Light and electron microscopic examination revealed pathological changes in the retinae and optic nerves consistent with chronic stages of acrylamide toxicity. Ophthalmic examination and light microscopy did not reveal abnormalities in the retinae or optic nerves in either the rest of the cattle from the herd or in offspring of exposed cattle.     

Systemic hypertensive disease and the feline fundus

The fundoscopic appearance and some of the histopathological findings of arterial hypertension in the cat are reviewed in relation to the anatomical and physiological features that place retinal function at particular risk when the eye is subjected to sustained increased arterial blood pressure. The fundus changes fall into three categories: hypertensive retinopathy, hypertensive choroidopathy and hypertensive optic neuropathy, and information from cases with confirmed arterial hypertensive disease is used to provide a basis for discussion and future investigation.     

Variability of resting endoscopic grading for assessment of recurrent laryngeal neuropathy in horses

Reasons for performing study: The extent to which variability affects endoscopic grading of arytenoid cartilage movement is uncertain. Objective: To determine the observer and within horse variability of grading arytenoid cartilage movement in horses during resting endoscopic examination, using a 7‐grade system. Methods: Endoscopic recordings of the upper respiratory tract made at rest in 270 draught horses were reviewed independently by 2 veterinarians to assess interobserver variability when scoring horses' laryngeal function with a 7‐grade system. Grading was repeated by both examiners in 80 randomly selected recordings in order to assess intraobserver variability. In 120 horses, endoscopy was repeated after 24–48 h, with videos graded by both veterinarians to assess intrahorse variability. Results: The mean weighted κ statistic for concordance within examiners was 0.867, with a mean intraobserver agreement of 76.3%. The weighted κ statistic for concordance between the 2 examiners was 0.765, with an interobserver agreement of 63.1%. Of the horses receiving 2 endoscopic examinations, the same grade was assigned to 57.1% of horses at the second examination, when effects resulting from interobserver variability were removed. The mean weighted κ statistic for concordance between the grade assigned at first vs. second examinations was 0.588, indicating only moderate agreement. Conclusions and potential relevance: Intra‐ and interobserver reliability of resting endoscopic grading of arytenoid cartilage movement using a 7‐grade system was high when examinations were conducted by experienced veterinarians. However, there was moderate daily intrahorse variability, suggesting that results of resting endoscopic examinations performed on a single day should be interpreted with caution.