Inclusion criteria and ethical considerations
This prospective descriptive study included dogs with naturally occurring PH referred to the Veterinary Teaching Hospital of the University of Helsinki (VTHUH) from March 2017 to December 2020. All PH cases were confirmed at the VTHUH based on rectal palpation before being included in the study. This paper is part of a larger research project assessing the etiology and treatment of canine perineal hernia. The population of dogs in the present study also includes a cohort of male dogs from a previously published study . We excluded dogs that had severe renal, hepatic, or cardiac disease or had an American Society of Anesthesiologists physical status rating of 4 or 5. Dogs that had previously undergone surgical treatment for PH were excluded.
Ethical permission for this research was provided by the Finnish national Project Authorization Board: ESAVI/4467/04.10.07/2017. Owners gave written consent for their dogs to take part in the study and had the possibility to withdraw at any time.
Upon entering the study, owners were required to complete a questionnaire, which included five sections: signalment, current GI signs, current urinary signs, history of GI signs and diseases, and history of non-GI diseases. The castration status (intact, castrated, and received hormonal treatment) and age of possible castration was also noted. The type of diet fed (commercial, home-cooked, raw, commercial and home-cooked, commercial and raw, other) before PH related clinical signs and the time since the latest deworming (months) were recorded.
Current GI signs included questions on inappetence, vomiting, diarrhea, tenesmus, defecating small quantities at a time, problems evacuating the bowel, staying in the defecating position for longer than usual, constipation, thickened stool, mucus in the stool, and blood in the stool. In addition, fecal incontinence, rectal prolapse, and swelling or bulging in the perineal area were recorded (yes/no/not sure). The duration of current GI signs associated with PH was evaluated (< 2 weeks, 2–4 weeks, > 4 weeks but < 3months, 3–6 months, > 6 months, not sure). The current urinary signs noted were pollakiuria, stranguria, dysuria, hematuria, and urinary incontinence (yes/no/not sure).
To assess the history of chronic GI signs and diseases, owners were asked to evaluate clinical signs occurring before the GI signs associated with PH that lasted for more than 3 weeks. The clinical signs asked about were vomiting, diarrhea, flatulence, blood or mucus in the feces, and constipation. In addition, owners were asked about any previous diseases diagnosed by a veterinarian such as GI diseases (colitis, proctitis, inflammatory bowel disease, food sensitivity, tylosin-responsive diarrhea), orthopedic diseases (hip joint laxity or dysplasia, pelvic or spinal fractures, degenerative changes in the lumbar vertebra or the LS junction), neurological conditions (e.g., intervertebral disc disease or a generalized neurological condition), anal sac inflammation or impaction, as well as tumors around the anus. Previously diagnosed gastrointestinal, orthopedic, and neurological diseases were categorized as “yes”, “no”, or “not sure”.
Evaluation of dogs
The dogs underwent a physical examination and a bloodwork assessment, including a complete blood count and serum biochemistry to evaluate the eligibility for the study. These were performed by a PhD researcher in clinical veterinary medicine with a degree in veterinary medicine (TÅ). The final inclusion of dogs in the study was based on the inclusion criteria and decided by an ECVS-certified veterinary surgeon (SM), who also conducted the orthopedic examinations. The neurological examination and the EMG and MNCV studies were conducted by an ECVN-certified veterinary neurologist (TSJ). The dogs were anesthetized and EMG, MNCV, and CT studies were conducted, after which they underwent PH surgery, including prescrotal castration if intact. CT images were analyzed by a veterinarian experienced in diagnostic imaging (HS).
A visual lameness evaluation (no lameness, mild lameness or minor gait abnormality, moderate lameness or obvious gait abnormality, severe weight-bearing lameness, non-weight-bearing
lameness) and an evaluation of the dogs’ muscle condition (normal, atrophied) were carried out. The spine was palpated for a pain reaction (yes/no) in the neck, back, or LS area. The joints of the thoracic and pelvic limb were evaluated for pain, swelling, crepitation, instability, and decreased range of motion (yes/no). The stifles were additionally evaluated for possible patellar luxation (yes/no, and if yes, the grade on a scale from I–IV), as well as a positive tibial compression or cranial drawer tests (yes/no).
The neurological examination included evaluation of the dogs’ mental status, posture, gait, assessment of postural reactions, spinal reflexes including perineal reflex and bulbourethral reflex, and finally, evaluation of cranial nerves. A scale from 0 to 3 (absent, decreased, normal, increased) was used for evaluating postural reactions and spinal reflexes. The panniculus reflex (normal, absent, abnormal) was considered normal if absent in an otherwise neurologically healthy dog and abnormal if there was a cut-off point .
For anesthesia, the dogs received intramuscular premedication with 0.3 mg/kg methadone (Insistor vet® 10 mg/mL; Richter Pharma AG, Wels, Austria) and 0.02 mg/kg acepromazine (Plegicil® 10 mg/mL; Bela-Pharm GmbH & Co KG, Vechta, Germany). Propofol (Propovet Multidose 10 mg/mL; Fresenius Kabi AB, Uppsala, Sweden) was given 1–4 mg/kg to effect and anesthesia was maintained with sevoflurane (end-tidal concentration 2.3%) in oxygen.
We performed all electrophysiological examinations with a Cadwell electrodiagnostic machine (Cadwell Industries, Inc., Kennewick, WA). EMG was performed bilaterally in the proximal and distal muscles of the pelvic and thoracic limbs, the paraspinal muscles and the perineal musculature. A disposable concentric needle electrode was used for EMG analysis and a subdermal needle electrode placed subcutaneously on the animal’s flank served as the ground. Abnormalities detected included abnormal insertional activity and any abnormal spontaneous activity such as fibrillation potentials and positive sharp waves.
MNCV of ulnar and peroneal nerves was measured unilaterally, performed with two stimulating monopolar needle electrodes. Subdermal needle electrodes served as a recording electrode, a reference electrode, and a ground electrode. Electrophysiological data were interpreted in comparison with published values [22,23,24]. The rectal temperature of the dog was measured during the electrodiagnostic testing.
Dogs underwent a CT scan using a helical 64-slice multidetector CT scanner (Lightspeed VCT, GE Healthcare, Madison, WI, USA) with a voltage of 120 kV, collimation pitch 0.516, speed 20.62 mm/rotation, rotation time 0.6 s, detector coverage 40 mm, matrix 512 × 512, and slice and interval thickness 0.625 mm. Using automodulation, the maximum current varied between 650 and 750 mAs. Dogs were in dorsal recumbency with hindlimbs in the “frog position” and scanned from the middle of the fourth lumbar vertebra to the most caudal aspect of the dog. Contrast agent 2 mL/kg (Omnipaque® 300 mg/mL) was injected into the vena cephalica using a power injector (Medrad® Stellant CT Injection System, Bayer AG, Leverkusen, Germany), and contrast scans were taken 1 min after the beginning of the injection.
CT images were assessed using a commercially available DICOM image processing workstation (Osirix®, v 11.0.4, Pixmeo, Switzerland) in MPR reconstruction. The lumbosacral spine was evaluated for intervertebral disc protrusion, as well as partial intervertebral foramen occlusion, using soft tissue windowing (window level 40, width 400). Any possible intervertebral disc protrusion was recorded and, if present, the disc space (L4-S1) and the percentage of protrusion into the spinal canal [none/minimal, slight (< 25%), moderate (25–50%), severe (> 50%)] were noted . In the presence of protrusion, signs of compression such as any shift of the epidural fat or asymmetry in the shape of the spinal cord or cauda equina on transverse images were recorded. If these signs of compression were absent, the protrusion was always classified as slight and deemed clinically irrelevant . In the case of partial occlusion of the intervertebral foramen, the severity (none, slight, moderate, and severe), type (soft tissue dense material, bone proliferation), disc space (L4-S1), and the location of the occlusion (left, right, or both) were assessed. The bony structures of the spine, pelvis, and hip joints were assessed using a bone window (window level 500, width 3500). The spine was assessed for vertebral anomalies and spondylosis, as well as signs of bone proliferation or irregularity of the sacroiliac joint (no/yes). The LS area was assessed for a visually obvious LS step between vertebral bodies (no/yes) and, if present, the step was measured (insignificant if < 2 mm, significant if > 2 mm) .
Hip joints were assessed for signs of degenerative joint disease by assessing signs of periarticular bone proliferation (osteophytes, enthesophytes), subchondral sclerosis, or incongruency. The findings (no lesions/femoral head and acetabulum congruent, developing/only presenting osteophytes at the dorsal acetabular rim or femoral head, established/presenting severe sclerosis and incongruency of the femoral head and acetabulum) were noted .
Statistical analysis was performed by a PhD researcher (T.Å.) using IBM® SPSS® Statistics, version 27.0.1 (IBM corp.©, Armonk, NY, USA). The findings from questionnaires and orthopedic or neurological evaluation were presented as a percentage (n/n), while continuous variables were presented as the mean (± standard deviation (SD); range) if normally distributed, otherwise as the median (interquartile range (IQR); range). The Pearson’s chi-squared test was used to explore possible etiological mechanisms. The following were tested: raw food diet and constipation, urinary incontinence and neurological or CT findings, CT findings and perineal- or bulbourethral reflexes. P-values less than 0.05 were considered statistically significant.