A REVIEW OF HORNER'S SYNDROME IN CATS & DOGS

Introduction

Horner's syndrome is a neuro-ophthalmic condition seen in cats and dogs. It is a term used to define a group of clinical signs related to lesions disrupting the sympathetic innervation to the eye. Horner's syndrome is classified as first (central), second (preganglionic) or third order (postganglionic), according to where the lesion is located within the oculosympathetic pathway.

Neuroanatomy 

Sympathetic innervation to the eye is a three-neuron pathway (Fig. 1). 

1. First Order (Upper Motor) Neurons

The cell bodies located at hypothalamus and rostral mid-brain, projects axons through the brain stem and cervical spinal cord, where they synapse on second order neurons.

2. Second Order (Preganglionic) Neurons

The cell bodies are located in the lateral bodies of spinal cord grey matter at the level of T1-T3. The axons leave the spinal cord and join thoracic sympathetic trunk. It passes through the cervicothroacic and middle cervical ganglion. At the level of thoracic inlet, the sympathetic trunk fuses with vagus nerve within a common epineurium. The sympathetic trunk deviates and terminates in the cranial cervical ganglion, located ventromedial to the tympanic bulla. 

3. Third Order (Postganglionic) Neurons

The axons exit cranial cervical ganglion and form plexus around the internal carotid artery. Some of the fibers pass through the tympanic bulla on the ventral surface and post ganglionic fibers may continue with internal carotid artery and enter the cranial cavity via the tympanooccipital fissure and carotid canal. Once within the calvarium, postganglionic fibers course ventral to the trigeminal ganglion and exit with the ophthalmic branch of trigeminal nerve through the occipital fissure. The fibers become nasociliary and long ciliary nerve, which supplies to iris dilator muscle, muscles of the periorbita and eyelids. Cats have sympathetic innervation of smooth muscles within the third eyelid, a feature that is absent in the dogs. 

Clinical Signs

The lack of sympathetic innervation to the eye results in following clinical signs (Fig 2 and Fig 3):

1. Miosis

When the sympathetic pathway is compromised, the inhibitory effect of the parasympathetic innervation to iris dilator muscle further prevents pupil dilation and exacerbates the miosis. As a result, anisocoria develops. Pupillary light reflex and vision remains intact in the affected eye. 

2.Ptosis

Ptosis develops because of loss of sympathetic tone in the thin muscles of the eyelids.

3. Enophthalmos 

The periorbital smooth muscles help maintain globe in the anterior position within the orbit. When these muscles relax without sympathetic input, the retractor bulbi muscles are without antagonism and they actively retract the globe in to orbit, producing enophthalmos. 

4. Third eyelid protrusion

The protrusion is passive in dogs and secondary to enophthalmos. In cats, its mainly due to sympathetically mediated smooth muscles in the third eyelid. 

First order Horner's syndrome is associated with diseases affecting hypothalamus, brain stem and cervical spinal cord. The most common causes are trauma, neoplasia, infection, inflammation and cervical intervertebral disc protrusion.

Second order Horne's syndrome appears secondarily to lesions in the T1-T3 spinal cord segments, or in the cranial thoracic sympathetic trunk towards the cranial cervical ganglion. The common causes are trauma, neoplasia, cranial mediastinal mass (thymoma/lymphoma) and brachial plexus avulsion. Signs associated with second order Horner's syndrome may include ipsilateral thoracic limb paresis/paralysis and loss of contraction the ipsilateral trunci muscle.

Third order Horner's presents secondarily to the lesions affecting the sympathetic pathway from the cranial cervical ganglion to the orbit. The common causes are otitis media/interna, vestibular disease, retrobulbar injury and neoplasia. Third order Horner's syndrome has also been reported as a complication to total ear canal ablation combined with lateral bulla osteotomy (TECA+LBO). 

Systemic diseases such as hypothyroidism, diabetes mellitus, lymphoma and Neospora canis infection have also been associated with Horner's syndrome. 

Diagnosis

Many ophthalmologists use the minimal dilation of miotic pupil to parasympatholytic (Tropicamide) and complete ophthalmological examination to rule out subtle uveitis and keratitis. For localization of the lesion, a dilute direct sympathomimetic (Phenylephrine) is instilled in both eyes. If the lesion is postganglionic (third order Horner's), a drop of 1% phenylephrine will create pupillary dilation, resolve enophthalmos, third eyelid protrusion and ptosis in under 20 minutes, while it will not dilate the normal pupil. When the Horner's syndrome is presented for longer than 3 weeks and the pupil fail to respond to 1% phenylephrine, bilateral instillation of 1 drop of 10% phenylephrine is pursued and again the response is timed. Both the normal and affected pupil should dilate within 20 minutes, the lesion is localized as postganglionic (third order Horner's). If the response time is between 20-45 minutes, the lesion is localized as preganglionic (second order Horner's). If the response time is more than 45 minutes or no resolution, then the lesion is localized as upper motor neuron (first order Horner's). 

Ancillary Diagnostics 

Further diagnostics are warranted to investigate the etiology of Horner's syndrome. In case of post ganglionic lesions, a thorough otoscopic examination should be performed. A complete blood count and serum biochemistry are advisable, to rule out metabolic disorders such as hypothyroidism and diabetes mellitus. Cervical and thoracic radiographs are indicated in cases of preganglionic lesions. Magnetic Resonance Imaging (MRI) or Computed Tomography (CT) is warranted in all cases of central lesions.

Treatment and Prognosis

Treatment and prognosis are dependent upon the underlying etiology. Symptomatic treatment with 1% or 10% phenylephrine can be used for short-term improvement of signs. Since there is no specific etiology for idiopathic Horner's syndrome, there is no specific treatment. Most cases of idiopathic Horner's will show improvement within several weeks to months. When permanent deficits occur, they are largely considered to be cosmetic with minimal to no impact on patient's quality of life. 

References 

1. Susan T.M. "Loss of vision and pupillary abnormalities." In: Small Animal Internal Medicine. 5th Ed. Edited by Nelson R.W. and Couto G.C., St. Louis, Missouri, U.S.A. (2014): 1013-1015.

2. Troxel Mark. "Horner syndrome at a glance." Clinician's Brief. May (2014): 25.

3. Tetas Roser and Bujan Diaz Jesus. "Neuro-ophthalmology: The approach to Horner's syndrome." Vet CPD Vol.6 (4) (2020): 34-35.  

4. Zwueste, Daneille M.,  and Bruce H. Grahn. "A review of Horner's syndrome in small animals." The Canadian Veterinary Journal 60.1 (2019): 81. 

 

MICROCHIPPING FOR PET DOGS

Few months ago, I came across the story of a dog named 'Alaska' reuniting with his owner after being lost for six years at Tucson, Arizona. I was so surprised to know that microchips helped several such pet parents to be reunited with their lost pets. When I started reading more about microchips, I strongly felt that there is a need to make more pet owners aware of this existing technology.   

The dog is man's best friend - one that may have an urge to wander, explore and runs the risk of getting lost. Unfortunately, it is not too uncommon for dogs to lose their way back home and end up in shelters. A staggering number of dogs are lost in shelters each year because there is a lack of reliable means for identification once they are found. If your pet is lost, you are far more likely to be reunited if they are microchipped. 

What is a microchip?

A microchip is a small, electronic chip enclosed in a glass cylinder that is about the same size as a grain of rice. Once the microchip is implanted under the skin, it will remain for entirety of your dog's lifetime. The chip contains a unique 15-digit number for identification, similar to aadhaar number for individuals. When scanned, the chip transmits its identification number using passive RFID (Radio Frequency Identification) technology on to the scanner, which displays the number on a screen.

The International Standards Organisation (ISO) has approved and recommended a global standard for microchips that ensures a consistent identification system worldwide. The ISO standard frequency is 134.2 kHz. Also, contrary to popular belief, the microchip is not a GPS device and cannot track your animal if it gets lost. The chip is RFID which enables it to be read by a microchip scanner, but only once your pet has been found.

Procedure

It is a 2 step process wherein chip is implanted and then the unique identification number is registered along with all the relevant details about the owner and the pet. Microchip comes pre-loaded in a sterile inject applicator. The chip is injected subcutaneously (just under the skin) between the shoulder blades using a hypodermic needle at the back of your pet's neck by a registered veterinarian.  It is no more painful than a typical injection, although the needle is slightly larger than those used for injections. No surgery or anesthesia is required and the microchip can be implanted during any regular vet check-ups. Make sure to read the chip right after injection using a microchip scanner. Also, ask your veterinarian to scan your pet's microchip at least once every year to make sure it is still detected. Having a microchip placed is only the first step, and the microchip must be registered in a central database and keep your registration information up-to-date. 

Why microchip your pets?

1. Unique Identity.  The microchip acts as the unique identification of your pet. The chip stores only a 15-digit unique number. This number is mentioned on all the records for the pet. Most pets wear collar tags imprinted with their name and the phone number of their owner, but only a microchip provides permanent ID that cannot fall off or be removed.

2. Find lost pets. If your pet is lost, you are far more likely to be reunited with they are microchipped as they can be scanned at nearest vets and the owner details can be obtained from the database. A study of more than 7,700 stray animals at animal shelters showed that dos without microchips were returned to their owners 21.9% of the time, whereas microchipped dogs were returned to their owners 52.2% of the time.

3. Travel. Microchipping is mandatory for international travel and recommended for travel within India. All pet documents must have microchip number.  

4. Pet insurance. Microchip is mandatory for buying pet insurance. 

5. Pet Registration. Every dog registered with KCI (Kennel Club of India) must compulsorily be microchipped.

As per The Prevention Cruelty to Animals (Dog Breeding and Marketing) Rules, 2017 and The Prevention of Cruelty to Animals (Pet Shop) Rules, 2018, no puppy can be sold by a breeder without a microchip. Also, microchipping can be one of the most effective ways to solve the cases of theft, abandonment and illegal pet trafficking.  

Conclusion 

A microchip is non-bio reactive and hence, biologically safe for the pet. It is a one-time investment with several benefits. The concept of microchipping for pet safety is not new, but pet owners in India are slowly becoming aware of it and the microchipping of pet dogs will be made compulsory in the days to come. Microchipping is also recommended in pet cats.

References 

1. https://petchipindia.org/

2. https://www.avma.org/resources-tools/pet-owners/petcare/microchips-reunite-pets-families/microchipping-faq

3. Lord, Linda K., et al. "Characterization of animals with microchips entering animal shelters". Journal of the American Veterinary Medical Association 235.2 (2009): 160-167.  

4. https://www.kgun9.com/news/local-news/missing-dog-reunited-with-owner-after-six-years

5. The Prevention Cruelty to Animals (Dog Breeding and Marketing) Rules, 2017

6. The Prevention of Cruelty to Animals (Pet Shop) Rules, 2018

 SURGICAL MANAGEMENT OF TRAUMATIC INTESTINAL EVISCERATION DUE TO INDIAN BISON (GAUR) ATTACK IN A DOBERMAN

    It was Dr. Shruti Gogia's last day at WVS India, Ooty and we were having dinner at the lecture hall on 16th April, 2022. At around 9:30 pm, a 9 month old, female, Doberman named  Puppy was presented with a history of devastating trauma caused by Indian bison (gaur). Evisceration of intestines was apparent (Fig 1). Many of these patients cannot be saved due to massive devitalisation of the bowel, infection and secondary injuries, some of the cases can be treated with aggressive medical and surgical management. We left the dinner plates on the table to attend this emergency.

    The treatment plan included – 1. Emergency triage and stabilization of the patient 2. Wound decontamination 3. Surgical correction and 4. Post-operative management. An IV catheter was placed and the patient was stabilized with IV fluids, antibiotics (Amox-Clav and Metronidazole) and Pain medication (Buprenorphine and Ketamine). Intestinal loops were assessed for viability and perforation. Intestinal loops were bright red in colour, and there was presence of intestinal peristalsis. Arterial pulsations in the mesenteric arteries were noticed. Warm saline lavage was done to remove the dirt and the intestines were covered with wet pads. There were no abnormalities in the blood report and radiographs.

    The dog was stable and the vital parameters were within normal range. The dog was placed in the lateral recumbency and the skin around the eviscerated loop was prepared aseptically with chlorhexidine solution. Puppy was induced with Diazepam and Propofol, and the endotracheal intubation was performed. General anaesthesia was maintained using Isoflurane gas anesthesia by Dr. Mukesh. A Lignocaine + Ketamine CRI was also used during the surgery. The intestinal loops were reduced into the abdominal cavity. The muscle layer were closed using 1-0 polydioxanone (PDS) in a simple continuous manner (Fig 2). The subcutaneous layer was closed in a continuous manner. The skin was opposed by cruciate suture pattern with 2-0 Polyamide (Nylon). 

    Following the surgery, Puppy was put on a course of antibiotics (Amox-Clav and Metronidazole) and pain killers (Meloxicam and Buprenorphine). An Elizabethan collar was used to prevent Puppy from biting or licking her surgical site. Strict rest and short leash walks were recommended for 2 weeks. Puppy made an uneventful recovery and the skin sutures were removed after 10 days. 

    Bison, boar and leopard attack cases are not so uncommon in Nilgiris. The pet owners need to carefully supervise their dogs when left outside to prevent such incidence. Dr. Shruti's last day at work was nothing less of an adventure. We were all extremely happy that puppy survived that night and made a recovery without complications. It was one last time the trio consisting of Dr. Shruti, Dr. Mukesh and myself were involved in a Friday night emergency!

References

 

1. Gower, Sara B., Chick W. Weisse, and Dorothy C. Brown. "Major abdominal evisceration injuries in dogs and cats: 12 cases (1998-2008)."Journal of American Veterinary Medical Association 234.12(2009): 1566-1572.

2. Slatter, Douglas H., ed. Textbook of small animal surgery. Vol. 1 & 2. Elsevier health sciences, 2003.

3. Stanley, Bryden J. "Complications of Intestinal Surgery WSAVA/FECAVA/BSAVA World Congress 2012."