Diagnostic utility of clinical and laboratory test parameters for differentiating between sudden acquired retinal degeneration syndrome and pituitary-dependent hyperadrenocorticism in dogs

Olfaction evaluation in dogs with sudden acquired retinal degeneration syndrome

PURPOSE

To evaluate olfaction in dogs with sudden acquired retinal degeneration syndrome (SARDS) compared with sighted dogs and blind dogs without SARDS as control groups.

ANIMALS STUDIED

Forty client-owned dogs.

PROCEDURE

Olfactory threshold testing was performed on three groups: SARDS, sighted, and blind/non-SARDS using eugenol as the test odorant. The olfactory threshold was determined when subjects indicated the detection of a specific eugenol concentration with behavioral responses. Olfactory threshold, age, body weight, and environmental room factors were evaluated.

RESULTS

Sixteen dogs with SARDS, 12 sighted dogs, and 12 blind/non-SARDS dogs demonstrated mean olfactory threshold pen numbers of 2.8 (SD = 1.4), 13.8 (SD = 1.4), and 13.4 (SD = 1.1), respectively, which correspond to actual mean concentrations of 0.017 g/mL, 1.7 × 10-13  g/mL and 4.26 × 10-13  g/mL, respectively. Dogs with SARDS had significantly poorer olfactory threshold scores compared with the two control groups (p < .001), with no difference between the control groups (p = .5). Age, weight, and room environment did not differ between the three groups.

CONCLUSIONS

Dogs with SARDS have severely decreased olfaction capabilities compared with sighted dogs and blind/non-SARDS dogs. This finding supports the suspicion that SARDS is a systemic disease causing blindness, endocrinopathy, and hyposmia. Since the molecular pathways are similar in photoreceptors, olfactory receptors, and steroidogenesis with all using G-protein coupled receptors in the cell membrane, the cause of SARDS may exist at the G-protein associated interactions with intracellular cyclic nucleotides. Further investigations into G-protein coupled receptors pathway and canine olfactory receptor genes in SARDS patients may be valuable in revealing the cause of SARDS.

[Urinalysis in dogs and cats, part 1: physical and chemical urinalysis]

The urinalysis of dogs and cats is an important part of the diagnostic evaluation of urinary tract diseases as well as for the identification of systemic diseases. A routine urinalysis consists of a physical and chemical examination of the urine as well as an examination of the urine sediment. Various urine collection methods (free-catch, catheterization, cystocentesis) are available. Each method has multiple advantages and disadvantages. The appropriate method must be chosen individually for each patient depending on the emphasis of the examination. The urine should ideally be examined within 30 minutes of collection as it is prone to change due to time and storage. Physical examination of the urine consists of the determination of urine color, clarity, and specific gravity which provides information regarding the concentration of the urine. The latter is determined by refractometry and needs to be interpreted in the context of the hydration status of the patient. Chemical examination of the urine consists of the determination of the pH value and the presence of blood/hemoglobin/myoglobin, protein, glucose, bilirubin, urobilinogen, nitrite, and ketones. The use of commercially available urine dipsticks is common. These must be stored and used according to the manufacturer's instructions and when interpreting the results, veterinary aspects need to be taken into consideration. The physical and chemical examinations of the urine represent rapid and readily performable methods that provide important information for the diagnosis or the exclusion of numerous diseases.

Hemostatic profiles in dogs with sudden acquired retinal degeneration syndrome

BACKGROUND

Sudden acquired retinal degeneration syndrome (SARDS) is a common cause of irreversible blindness in dogs. It bears clinical resemblance to hypercortisolism, which can be associated with hypercoagulability. The role of hypercoagulability in dogs with SARDS is unknown.

OBJECTIVE

Determine hemostatic profiles in dogs with SARDS.

ANIMALS

Prospective pilot study: Dogs with a history of SARDS (n = 12). Prospective case-control study: Dogs with recent onset of SARDS (n = 7) and age-, breed-, and sex-matched controls (n = 7).

METHODS

Prospective pilot study: We performed thromboelastography (TEG). Prospective case-control study: Dogs had CBC, serum biochemistry, urinalysis, TEG, fibrinogen concentration, antithrombin activity, D-dimers, thrombin-antithrombin complexes, and optical platelet aggregometry performed.

RESULTS

Prospective pilot study: 9/12 dogs with a history of SARDS were hypercoagulable with increased TEG G value and 2/3 had hyperfibrinogenemia. Case-control study: All dogs with SARDS and 5/7 controls were hypercoagulable based on TEG G value. Dogs with SARDS had significantly higher G values (median, 12.7 kdynes/s; range, 11.2-25.4; P = .04) and plasma fibrinogen concentration (median, 463 mg/dL; range, 391-680; P < .001) compared to controls.

CONCLUSIONS AND CLINICAL IMPORTANCE

Hypercoagulability was common in both dogs with SARDS and controls, but dogs with SARDS were significantly more hypercoagulable on TEG. The role of hypercoagulability in the pathogenesis of SARDS remains to be determined.

Outer retinal thickness and visibility of the choriocapillaris in four distinct retinal regions imaged with spectral domain optical coherence tomography in dogs and cats

Purpose

To evaluate the outer retinal band thickness and choriocapillaris (CC) visibility in four distinct retinal regions in dogs and cats imaged with spectral domain optical coherence tomography (SD‐OCT). To attempt delineation of a fovea‐like region in canine and feline SD‐OCT scans, aided by the identification of outer retinal thickness differences between retinal regions.

Methods

Spectralis® HRA + OCT SD‐OCT scans from healthy, anesthetized dogs (n = 10) and cats (n = 12) were analyzed. Scanlines on which the CC was identifiable were counted and CC visibility was scored. Outer nuclear layer (ONL) thickness and the distances from external limiting membrane (ELM) to retinal pigment epithelium/Bruch's membrane complex (RPE/BM) and ELM to CC were measured in the area centralis (AC), a visually identified fovea‐like region, and in regions superior and inferior to the optic nerve head (ONH). Measurements were analyzed using a multilevel regression.

Results

The CC was visible in over 90% of scanlines from dogs and cats. The ONL was consistently thinnest in the fovea‐like region. The outer retina (ELM‐RPE and ELM‐CC) was thickest within the AC compared with superior and inferior to the ONH in dogs and cats (p < .001 for all comparisons).

Conclusions

The CC appears a valid, albeit less than ideal outer retinal boundary marker in tapetal species. The AC can be objectively differentiated from the surrounding retina on SD‐OCT images of dogs and cats; a fovea‐like region was identified in dogs and its presence was suggested in cats. These findings allow targeted imaging and image evaluation of these regions of retinal specialization.

Comparison of the qualitative and quantitative optical coherence tomographic features between sudden acquired retinal degeneration syndrome and normal eyes in dogs

OBJECTIVE

To quantitatively and qualitatively characterize the retinal optical coherence tomographic features of sudden acquired retinal degeneration syndrome (SARDS) and SARDS suspect dogs.

ANIMALS STUDIED

Fourteen SARDS affected dogs, 11 age-, breed-, and sex-matched control dogs, and two SARDS suspect dogs.

PROCEDURES

Spectral-domain optical coherence tomography (OCT) images were used to evaluate the quantitative features, including thickness, intereye asymmetry, and longitudinal changes in retinal layer thickness and the qualitative features, including retinal architecture and vitreous haze.

RESULTS

Mean outer retinal layer thickness (ORT), outer nuclear layer thickness (ONL), and photoreceptor layer thickness (PRL) were significantly lower in the SARDS group, whereas mean inner retinal layer thickness was significantly higher in the SARDS group than in the control group. While thickness values of all retinal layers did not differ significantly between paired eyes in each group, the absolute intereye asymmetries in the ORT (p < .0001), ONL (p = .008), and PRL (p < .0001) were significantly higher in the SARDS group than in the control group. Some SARDS patients and SARDS suspects had a greater PRL than the control group, and serial OCT evaluation showed an increase in PRL in one SARDS suspect. Vitreous haze severity was greater in the SARDS group than in the control group (vitreous relative intensity, p = .030).

CONCLUSIONS

We described the OCT features of SARDS patients and suspects. In particular, PRL thickening in the SARDS suspects might indicate an early change in SARDS. Although further studies are needed, this finding might provide new insights into the pathogenesis of SARDS.

Ocular abnormalities in Polish Hunting Dogs

This study aimed to describe and determine the prevalence of ocular abnormalities in Polish Hunting Dogs. The study was conducted with 193 Polish Hunting Dogs: 101 female and 92 male animals, aged between 3 months and 12 years. Ophthalmic examinations were performed using slit lamp biomicroscopy, ophthalmoscopy, and tonometry based on the ophthalmological protocol for the examination of hereditary eye diseases. Spectral-domain optical coherence tomography (SD-OCT) was performed for dogs with sudden acquired retinal degeneration syndrome (SARDS) and progressive retinal atrophy (PRA), while electroretinography was also performed in dogs with SARDS. Five dogs (2.6%) were diagnosed with cataract, iris coloboma in 3 dogs (1.6%), ocular dermoid in 1 dog (0.5%), and retinal dysplasia, distichiasis and entropion in 1 dog (1%). Three dogs (1.6%) were diagnosed with PRA and SARDS occurred in 1 dog. Retinal lesions was observed in 16 dogs (8.3%). The clinical signs of retinopathy observed in Polish Hunting Dogs included discoloration of the tapetal fundus, patchy increased reflectivity in the region of discoloration, focus of hyperpigmentation and an area of tapetal hyper-reflectivity with a pigmented center. SD-OCT performed in the 3 dogs with PRA revealed alteration in the retinal layers, which was most advanced in the non-tapetal fundus. Although SD-OCT revealed retinal layers with normal architecture only in some parts of the dorsal, nasal and temporal regions in dogs with SARDS, areas of disorganized external limiting membrane, myeloid zone, ellipsoid zone, outer photoreceptor segment and interdigitation zone were also observed. Polish Hunting Dogs should undergo periodic ophthalmological examination for the evaluation of other hereditary eye diseases. The prevalence of retinal lesions in Polish Hunting Dogs requires further research.

Development of retinal bullae in dogs with progressive retinal atrophy

OBJECTIVE

To report the development of focal bullous retinal detachments (bullae) in dogs with different forms of progressive retinal atrophy (PRA).

PROCEDURES

Dogs with three distinct forms of PRA (PRA-affected Whippets, German Spitzes and CNGB1-mutant Papillon crosses) were examined by indirect ophthalmoscopy and spectral domain optical coherence tomography (SD-OCT). Retinal bullae were monitored over time. One CNGB1-mutant dog was treated with gene augmentation therapy. The canine BEST1 gene coding region and flanking intronic sequence was sequenced in at least one affected dog of each breed.

RESULTS

Multiple focal bullous retinal detachments (bullae) were identified in PRA-affected dogs of all three types. They developed in 4 of 5 PRA-affected Whippets, 3 of 8 PRA-affected Germans Spitzes and 15 of 20 CNGB1-mutant dogs. The bullae appeared prior to marked retinal degeneration and became less apparent as retinal degeneration progressed. Bullae were not seen in any heterozygous animals of any of the types of PRA. Screening of the coding region and flanking intronic regions of the canine BEST1 gene failed to reveal any associated pathogenic variants. Retinal gene augmentation therapy in one of the CNGB1-mutant dogs appeared to prevent formation of bullae.

CONCLUSIONS

Retinal bullae were identified in dogs with three distinct forms of progressive retinal atrophy. The lesions develop prior to retinal thinning. This clinical change should be monitored for in dogs with PRA.

Canine sudden acquired retinal degeneration syndrome: Owner perceptions on the time to vision loss, treatment outcomes, and prognosis for life

BACKGROUND

Canine sudden acquired retinal degeneration syndrome (SARDS) causes blindness for which there are no proven effective treatments. We aimed to clarify the time to vision loss, treatment response/side effects, and prognosis for life in dogs with SARDS.

METHODS

An online questionnaire was administered to owners of dogs with a historical diagnosis of SARDS. Mortality data were compared with a published purebred reference population. Select parameters were analyzed statistically using general linear model with least square means, two-sample t tests, and chi-squared or Fisher's exact tests.

RESULTS

Responses from owners that stated that their dog visited an ophthalmologist and had electroretinography performed (n = 434) were analyzed. The majority of owners (65.4%) reported the time from vision disturbance to complete vision loss as <2 weeks; 19.4% reported >4 weeks. Onset of systemic clinical signs to complete vision loss was >4 weeks in 44.5% of responses. A higher proportion of owners reported some vision recovery with combination treatment (14.4%) compared with monotherapy (3.2%, P = .0004). Side effects of treatment were commonly reported. Dogs with SARDS did not have a shorter lifespan than the reference population but had higher incidence of kidney disease (P = .0001) and respiratory disease (P = .0004) at death.

CONCLUSIONS

Dogs with SARDS have a rapid onset of vision loss. In the owner's opinion, treatment is unlikely to restore vision and is associated with systemic side effects. The potential for systemic pathologies that arise after SARDS diagnosis warrants further study.

Changes in retinal layer thickness with maturation in the dog: an in vivo spectral domain - optical coherence tomography imaging study

BACKGROUND

Retinal diseases are common in dogs. Some hereditary retinal dystrophies in dogs are important not only because they lead to vision loss but also because they show strong similarities to the orthologous human conditions. Advances in in vivo non-invasive retinal imaging allow the capture of retinal cross-section images that parallel low power microscopic examination of histological sections. Spectral domain - optical coherence tomography (SD-OCT) allows the measurement of retinal layer thicknesses and gives the opportunity for repeat examination to investigate changes in thicknesses in health (such as changes with maturation and age) and disease (following the course of retinal degenerative conditions). The purpose of this study was to use SD-OCT to measure retinal layer thicknesses in the dog during retinal maturation and over the first year of life. SD-OCT was performed on normal beagle cross dogs from 4 weeks of age to 52 weeks of age. To assess changes in layer thickness with age, measurements were taken from fixed regions in each of the 4 quadrants and the area centralis (the region important for most detailed vision). Additionally, changes in retinal layer thickness along vertical and horizontal planes passing through the optic nerve head were assessed.

RESULTS

In the four quadrants an initial thinning of retinal layers occurred over the first 12 to 15 weeks of life after which there was little change in thickness. However, in the area centralis there was a thickening of the photoreceptor layer over this time period which was mostly due to a lengthening of the photoreceptor inner/outer segment layer. The retina thinned with greater distances from the optic nerve head in both vertical and horizontal planes with the dorsal retina being thicker than the ventral retina. Most of the change in thickness with distance from the optic nerve head was due to difference in thickness of the inner retinal layers. The outer retinal layers remained more constant in thickness, particularly in the horizontal plane and dorsal to the optic nerve head.

CONCLUSIONS

These measurements will provide normative data for future studies.

Ophthalmic findings in sheep treated with closantel in Curitiba, Brazil

BACKGROUND AND AIM

Closantel is a widely used anti-parasitic drug that is known to cause ophthalmic problems that lead to blindness. The aim of this study was to investigate the possible electroretinographic changes in sheep that received closantel.

MATERIALS AND METHODS

Twenty-four 30-day-old Suffolk sheep were split into control group (12 animals) and closantel group (12 animals). The latter group received 15 mg/kg of closantel subcutaneously immediately after the first electroretinography (ERG). The ISCEV protocol was used to perform the ERGs pre-dose (0), 7, and 30 days after treatment. Statistical analyses to compare ERG responses using t-test and analysis of variance were performed (p<0.05). Three months later, the animals were euthanized and the eyes and a part of optic nerve were collected for histopathology. Photography of the retina and optic nerve was taken, and measures of the retinal layers were made and analyzed by paired t-test.

RESULTS

Closantel group showed a significant increase of the mean scotopic a-wave amplitude from 0 to 7 days after closantel administration, using a stimulus of 10,000 mcd.s/m2 and a decrease of the mean scotopic and photopic a-wave amplitude (from 7 to 30 days) using the same flash intensity, as well as a decrease in mean photopic b-wave amplitude (from 7 to 30 days) within the group. Control group showed a significant increase of the mean scotopic b-wave implicit time from pre to 30 days after treatment and an increase of the mean scotopic a-wave implicit time from pre to 7 days after treatment, with the stimulus of 10,000 mcd.s/m2. This group also showed a decrease in mean photopic b-wave implicit time (from pre to 30 days after treatment), using a stimulus of 10,000 mcd.s/m2 and a decrease in mean photopic a-wave implicit time from pre to 30 days after treatment, using a stimulus of 3000 mcd.s/m2. The no difference was found in images neither in the measurements of the retina layers.

CONCLUSION

As observed by ERG responses and the histopathology, a dose of 15 mg/kg of closantel does not significantly affect retinal and optic nerve structures in sheep but the electroretinographic results, however, showed alterations on the phototransduction.

Detection of circulating anti-retinal antibodies in dogs with sudden acquired retinal degeneration syndrome using indirect immunofluorescence: A case-control study

Sudden acquired retinal degeneration syndrome (SARDS) in dogs is proposed to have an immune-mediated etiology. However, there is conflicting evidence regarding the presence of antiretinal antibodies, as assessed by western blotting, in the serum of SARDS patients. Because of the possibility that antibodies recognize only conformational epitopes, we hypothesized that a more sensitive method to investigate circulating retinal autoantibodies in SARDS is immunofluorescence. Sera from 14 dogs with early SARDS, and 14 age- and breed-matched healthy control dogs were screened for circulating antiretinal IgG, IgM, IgE and IgA using indirect immunofluorescence on lightly fixed frozen sections of normal canine retina. Controls without canine serum were also performed. A nuclear counterstain was used to identify cellular retinal layers. Images were obtained using a fluorescence microscope, and 2-3 separate masked observers graded retinal layers for fluorescence staining intensity using a 0-3 scale. Total circulating IgG and IgM was assessed by radial immunodiffusion. Statistical analysis was performed using 2-way ANOVA, paired 2-tailed student's t-test and correlation analysis. Intensity of IgG staining of photoreceptor outer segments was significantly higher using serum from dogs with SARDS compared with healthy controls in 2/3 observers (P < 0.05). Intensity of IgM staining throughout the retina was higher in SARDS dogs compared to matched healthy controls (P < 0.0001), although no specific retinal layer was statistically significant. There were no differences in staining intensity for IgE or IgA. Dogs with SARDS had a comparably lower circulating IgG and higher IgM than healthy controls (P = 0.01 and 0.001 respectively) and IgG and IgM were negatively correlated (r = -0.69, P = 0.007). Despite having decreased serum IgG compared with healthy controls, circulating IgG in dogs with SARDS binds photoreceptor outer segments to a greater extent. Dogs with SARDS have a relatively higher circulating IgM than matched healthy controls. The pathogenic nature of these antibodies is unknown.

Circulating neurohormone imbalances in canine sudden acquired retinal degeneration syndrome and canine pituitary-dependent hypercortisolism

BACKGROUND

Sudden acquired retinal degeneration syndrome (SARDS) has clinical similarity to pituitary-dependent hypercortisolism (PDH) in dogs. Some studies have identified a greater frequency of SARDS in seasons with reduced daylight hours. Neurohormone imbalances contribute to retinal lesions in other species, warranting further study in dogs with SARDS.

HYPOTHESIS

Dysregulation of circulating melatonin concentration is present in dogs with SARDS but not in dogs with PDH.

ANIMALS

Fifteen client-owned dogs with spontaneous SARDS (median time of vision loss 18 days), 14 normal dogs, and 13 dogs with confirmed PDH.

PROCEDURES

Prospective case-control study. ELISA on samples (obtained in the morning) for measurement of plasma melatonin and dopamine, serum serotonin, urine 6-sulfatoxymelatonin (MT6s), and creatinine. Statistical analysis was performed using 1-way ANOVA, Spearman correlation and receiver operator characteristic area under the curve analysis.

RESULTS

There were no significant differences in circulating melatonin, serotonin or dopamine concentrations between the 3 groups, although the study was underpowered for detection of significant differences in serum serotonin. Urine MT6s:creatinine ratio was significantly higher in dogs with PDH (4.08 ± 2.15 urine [MT6s] ng/mL per mg of urine creatinine) compared with dogs with SARDS (2.37 ± .51, P < .01), but not compared with normal dogs.

CONCLUSIONS AND CLINICAL RELEVANCE

We have identified neurohormone differences between dogs with SARDS and PDH.