Schwannoma in Dogs
Nerve sheath tumors in dogs, specifically schwannomas, originate within the myelin sheath. The myelin sheath is generated by Schwann cells, specialized cells that envelop peripheral nerves. They offer mechanical support and insulation for the nerves, facilitating the transmission of electrical signals throughout the nervous system. The peripheral nervous system comprises nerves located outside the central nervous system, encompassing the brain and spine. The term “peripheral nerve sheath tumor” encompasses schwannomas, neurofibromas (nerve fiber tumors), neurofibrosarcomas (malignant nerve fiber tumors), and hemangiopericytomas (tumors affecting blood vessels and soft tissue). These tumors are believed to originate from the same cell type.
Symptoms and Types
- Chronic and progressive lameness in the forelimbs accompanied by muscle atrophy
- Lameness observed in the hind limbs
- Peripheral nerve disorder resulting from self-mutilation
- Detectable mass upon palpation (able to be felt through touch examination)
- Horner’s syndrome, a condition affecting the sympathetic nervous system, leading to automatic nerve reactions and impacting parts of the body not directly controlled consciously
- If the Schwannoma is located in the neck, symptoms may include:
- Drooping eyelid
- Facial paralysis on one side
- Constriction of pupil size
- Slight elevation of the lower eyelid
Causes
Idiopathic (of unknown origin)
Diagnosis
Your veterinarian will conduct a comprehensive physical examination of your dog, which includes a blood chemical profile, complete blood count, urinalysis, and electrolyte panel. You’ll be required to provide a detailed history of your dog’s health leading up to the appearance of symptoms. For detailed information about the extent and location of the disease, computed tomography (CT) or, preferably, magnetic resonance imaging (MRI) scans are recommended. An electromyogram, measuring muscle activity, will indicate abnormal muscle patterns if a schwannoma is present.
Treatment
The preferred treatment involves surgically removing (excising) the tumor. Amputation of the affected limb is often required, and it’s common to experience local recurrence post-surgery. In cases where the schwannoma involves nerve roots, a laminectomy (spinal surgery to alleviate pressure) is recommended. The potential effectiveness of radiotherapy depends on the extent of growth and should be discussed with your veterinarian.
Living and Management
Following surgical excision of a schwannoma, recurrence occurs in 72 percent of cases. When the tumor affects a limb, treatment becomes easier if it is closer to the paw. Schwannomas seldom metastasize to regional lymph nodes or the lungs, typically remaining localized within nerve cells.
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