Understanding Canine Chiari-Like Malformation

Canine Chiari-like malformation is a condition that affects the spine of dogs, causing a range of symptoms that can impact their quality of life.

The condition is characterized by a compression of the cerebellum, which is the part of the brain that controls balance and coordination.

The compression is caused by an abnormal formation of the foramen magnum, which is the opening at the base of the skull that allows the spinal cord to connect to the brain.

This compression can lead to a range of symptoms, including neck pain, weakness, and difficulty walking.

In some cases, the compression can also cause seizures, vision loss, and even paralysis.

Understanding the causes and symptoms of canine Chiari-like malformation is crucial for providing effective treatment and improving the lives of affected dogs.

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Canine Chiari-like malformation is a serious condition that affects some breeds, particularly the Cavalier King Charles Spaniel (CKCS). Approximately 50% to 70% of CKCS with this condition develop syringomyelia, a condition that can cause a range of symptoms.

The age of onset for symptoms is quite broad, ranging from younger than 6 months to older than 12 years, but most dogs start showing clinical signs between 3 and 6 years of age. This means that if you're a CKCS owner, it's essential to be aware of the potential for this condition to develop in your dog as they mature.

Some dogs may exhibit symptoms such as yelping when their head is touched or reluctance to climb stairs, as seen in Bert, a 6.5-year-old male CKCS who was referred for rehabilitation therapies to manage his symptoms.

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The signalment of a patient is a crucial piece of information that helps veterinarians understand their condition. In the case of Canine Multifocal Retinal Dysplasia (CM), it's estimated to affect up to 95% of the Cavalier King Charles Spaniel (CKCS) population.

CKCS dogs are particularly prone to CM, which often leads to syringomyelia, a condition where fluid-filled cavities form in the spinal cord. Approximately 50% to 70% of CKCS dogs with CM develop syringomyelia.

Clinical signs of CM typically start to appear in young adulthood, between 3 and 6 years of age. However, the age range can be quite broad, with some dogs showing symptoms as early as 6 months or as late as 12 years.

A 6.5-year-old male CKCS named Bert is a great example of this. He was referred for rehabilitation therapies to manage symptoms like yelping when his head was touched and reluctance to climb stairs.

Bert's medical history revealed a lack of proprioception, which is the ability to sense the position and movement of one's body. This was a significant concern for his owners.

His examination by the referring veterinary surgeon also showed signs of neck pain.

The clinical presentation of canine Chiari-like malformation (CMSM) can be quite challenging to identify, as the symptoms are often vague and variable.

Variable clinical signs are common in CMSM, and most often reflect manifestations of neuropathic pain (NP).

Neuropathic pain is pain caused by damage or disease affecting the somatosensory nervous system, leading to abnormal sensations or pain from normally nonpainful stimuli.

People who suffer from CMSM describe headaches, radiating pain affecting the arms and shoulder region, and paresthesia (pins and needles, burning or stretching sensations).

The most common clinical signs in dogs are "phantom scratching" and unprovoked vocalizations seemingly resulting from poorly localizing pain.

Phantom scratching is a behavior in which the patient exhibits scratching movements with the pelvic limb but does not actually make contact with the target body part.

Many patients clinically affected with CMSM do not exhibit abnormalities on a routine examination; presumptive diagnosis may be made on history alone.

Pain upon palpation of the atlanto-occiptal region is a consistent physical examination finding in these patients.

Other abnormalities noted on examination may include cervical or head pain on palpation, ataxia, tetraparesis, cranial nerve abnormalities, scoliosis, and proprioceptive deficits.

Clinical signs in humans with CM1 are similar to those in dogs, including pain, headaches, altered sensation, weakness, dysphagia, sleep apnea, sensory deficits, weakness of the extremities, and muscle atrophy.

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The pain experienced with SM has been characterized as central neuropathic pain (NeP), caused by direct damage to the dorsal horn and spinothalamic tract.

Dogs of all ages may present with symptomatic CM, but the most common signs develop in younger dogs at two to four years of age.

Symptomatic dogs can also present with CM without SM, and the most common signs reported with CM/SM are manifestations of generalized pain or pain localized to the spinal cord.

Symptoms may include spontaneous vocalization, sensitivity to palpation, and avoidance of pain-evoking movements/postures.

Behavioral changes such as increased anxiety are also common in dogs clinically affected with CM/SM.

Neuropathic pain can manifest itself through allodynia, hyperalgesia, and paresthesia, and "air guitar/phantom scratching" may be associated with dysesthesia or itch.

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Diagnosis of Canine Chiari-like Malformation can be challenging due to its overlapping nature with other diseases. MRI is the diagnostic tool of choice, as it shows caudal cerebellar herniation and compression, occipital dysplasia, and attenuation of CSF flow in the cranial cervical region.

Whole spine MR imaging may be used to evaluate the extent of syrinx formation in CM dogs, which appears as a linear hyperintensity within the spinal cord. This is especially useful in cases where the syrinx forms from C1 to C4.

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Diagnosis is a crucial step in determining the presence of Chiari-like malformation (CMSM) and syringomyelia (SM) in dogs. MRI of the brain and cervical spinal cord is the standard of care for diagnosis.

The imaging shows caudal cerebellar herniation and compression, occipital dysplasia, and attenuation of CSF flow in the cranial cervical region. This helps identify the malformation and its effects on the surrounding tissues.

Syringomyelia appears as a linear hyperintensity within the spinal cord, most commonly from C1 to C4. This can be a key indicator of the condition.

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Before MRI became widely available, diagnosis was challenging and often misdiagnosed as other conditions like allergic skin disorders or disk disease. Thermography may be a useful tool in the diagnosis of CMSM and SM, requiring no sedation or clipping of hair.

A recent study found that dogs are more likely to be diagnosed and treated if they are insured. However, even without a final diagnosis, veterinary practitioners can recognize pain in these patients and treat accordingly.

History and clinical signs aid in the diagnosis, especially for the presence of neuropathic pain (NeP). Quantitative sensory testing (QST) can be used to assess for NeP, applying a stimulus to an area of the body to quantify sensory or nociceptive thresholds.

Chronic pain scales, such as the Canine Brief Pain Inventory, can be useful for diagnosis and evaluating changes over time and the effects of treatment.

The pathophysiological mechanisms underlying a diagnosis can be complex, but let's break it down.

Inflammation is a key player in many diseases, and it can be triggered by a variety of factors, including infections, autoimmune responses, and physical injury.

Chronic inflammation can lead to tissue damage and organ dysfunction, making it a major contributor to many serious health conditions.

The release of pro-inflammatory cytokines, such as TNF-alpha and IL-1beta, plays a crucial role in the inflammatory process, causing blood vessels to become leaky and allowing white blood cells to infiltrate affected tissues.

Cancer cells often exploit the body's natural repair mechanisms to promote their own growth and survival, leading to uncontrolled cell proliferation and tumor formation.

The loss of normal cell-cell adhesion and the acquisition of migratory and invasive properties are key features of cancer cell behavior, enabling them to spread to distant sites and form metastases.

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Initial therapy for Canine Chiari-like malformation (CMSM) is medical management, aiming to reduce clinical signs and improve quality of life. This often involves a multimodal approach with a combination of drugs.

For young dogs with clinical signs, surgical removal is considered to minimize disease progression as the dog ages. Older dogs with little or no clinical signs may be treated medically instead.

Surgical intervention aims to restore normal cerebrospinal fluid dynamics via decompression of the caudal foramen magnum. One study found 80% of patients improved post-surgery.

Gabapentin, pregabalin, and tricyclic antidepressants are commonly used for neuropathic pain (NeP) in veterinary patients. Gabapentin has been shown to prevent the release of excitatory neurotransmitters, making it a beneficial treatment for NeP.

A recommended dose of gabapentin is 10-20 mg/kg every 8 hours, although the range of plasma concentrations associated with clinical effects is uncertain. The most frequent adverse effects in humans include dizziness, somnolence, and peripheral edema.

Corticosteroids, such as prednisone, are useful in the treatment of CMSM, especially for acute exacerbations. A short, anti-inflammatory dosing schedule of prednisone tapered down to the lowest effective dose is preferred.

Surgical intervention should be considered in patients with severe clinical signs, syringomyelia diameter >3 mm, or those who fail medical management. The primary goals of surgery are to improve patient comfort and slow or stop the progression of syringomyelia.

Decompressive surgery for CMSM is known as a foramen magnum decompression (FMD), which involves a suboccipital craniectomy and durotomy over the atlanto-occipital region. Studies have shown 80-94% of patients exhibit early postoperative improvement following FMD.

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Medical management of Canine Chiari-like malformation primarily revolves around treating neurological problems and reducing cerebrospinal fluid production.

In general, a multimodal or polypharmacy approach is the most effective way to treat neurological problems. Most patients show at least some improvement in symptoms with the addition of gabapentin or pregabalin.

The severity of clinical signs can be variable, and some patients with minimal symptoms may not necessarily require pain medication.

Corticosteroids, such as prednisone, are useful in the treatment of Canine Chiari-like malformation and may be most effective in patients experiencing a more acute exacerbation of the disease.

A short, anti-inflammatory dosing schedule of prednisone tapered down to the lowest effective dose is often preferred.

Amantadine may enhance the effectiveness of gabapentin, NSAIDs, or opioids in treating neurological problems and should be considered as a component of polypharmacy in severe cases.

Chiari-like malformation and syringomyelia are two linked conditions that cause neuropathic pain in dogs.

A high proportion of Cavalier King Charles Spaniels are affected by these conditions, although other breeds can also be susceptible.

Clinical signs of neuropathic pain are non-specific, making diagnosis challenging.

Confirmation of the disease is supported by magnetic resonance imaging.

Treatment options include using a combination of different analgesics, but neuropathic pain can be difficult to treat.

Surgical decompression of the caudal cranial fossa is another treatment option, but it's essential for owners to be aware of the challenges of treating this condition.

The main goal of treatment is to maintain a good quality of life for the patient.

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