Focus on Cervical Pain
By: Jim Cook, DVM, PHD, DACVIM
Specialists in Companion Animal Neurology – SCAN
Signalment and History
Tippy, a 6.6 kg, 7 1/2 year-old old FS Chihuahua mix, was presented to Specialists in Companion Animal Neurology (SCAN) for evaluation of cervical pain. Her owner reported that she had been having intermittent attacks of spasm and pain for 3 to 4 years that were triggered by sudden moves or vigorous activities. The attacks were quite painful but never affected her walking ability. The most recent attack was approximately 1 month prior to referral. Tippy’s current treatment included 2.5 mg prednisone every 48 hours, acupuncture and Chinese herbal formulas.
Neurological Exam and Initial Diagnostics
On presentation, Tippy was bright, alert and happily affectionate. Her gait, cranial nerves, postural reactions and reflexes were all normal but she was noticeably uncomfortable during palpation and manipulation of her cervical region.
Pain or hyperesthesia implies compression or inflammation of sensitive structures (bone/periosteum), soft tissues (ligaments/tendons/muscles), meninges and nerve roots. Pathology of the spinal cord itself does not typically create pain as the spinal cord is not supplied with nerve endings for pain perception; it is compression of the meninges that generates pain with spinal cord disorders. Differential diagnoses included: IVDH, inflammatory disease (e.g., GME/MUE), structural disease such as Chiari-like malformation/syringohydromyelia, and soft tissue injury (analogous to “whiplash” in humans). Each of these can have a protracted and/or intermittent time course. Approximately 30 percent of dogs with brain masses, or other causes of increased intracranial pressure, may present with cervical pain. The chronic, intermittent course over some years (without other detectable deficits) make this syndrome (or primary spinal neoplasia) in this patient unlikely.
A preanesthetic database of CBC/biochemical profile and thoracic radiographs had no significant abnormalities. An MRI of the skull and cervical spinal cord showed rostral and caudal flattening of the cerebellum with indentation of the cerebellar vermis (Figure 1, arrowhead). Syringohydromyelia was prominent at C3 and T2 (Figure 2). These findings are consistent with Chiari-like malformation (or Caudal Occipital Malformation Syndrome [COMS]) with syringomyelia (CM/SM).
MRI performed on 1-31-18
T2-weighted sagittal image of the brain showing moderate compression and coning of the caudal cerebellar vermis (arrow).
MRI performed on 1-31-18
T2-weighted sagittal image of the cervical spinal cord showing syrinx formation (syringohydromyelia) at C3 (left arrow) and T2 (right arrow).
Treatment, Outcome and Comments
Treatment can be conservative or surgical, depending on the age of the patient and the severity of clinical signs and SM. Some neurologists treat less severe cases with gabapentin, omeprazole, +/- intermittent low dose corticosteroid therapy as well as, other modalities, such as therapeutic laser. They report good long-term results. In more severe cases or patients that are refractory to medical management, surgery is recommended. Surgery consists of a “keyhole” enlargement of the foramen magnum to decompress the cerebellum and transection of the various fibrous bands that can develop, causing transverse compression of the medullospinal junction and spinal cord. If significant hydrocephalus is present from obstruction of cerebrospinal fluid flow, some surgeons will install a ventriculoperitoneal shunt; however this is rarely necessary.
CM/SM is most often seen in smaller dogs and toy breeds with a definite breed predilection for the Cavalier King Charles Spaniel. Compression of the meninges by a malformed caudal occipital region (and the various transverse fibrous bands which can be present) will cause pain. Syringomyelia is a chronic, progressive condition in which longitudinal fluid-filled cavities develop within the spinal cord at the expense of the normal sensory neurons. The distortion of spinal cord tissue can contribute to abnormal sensations (neuropathic pain) which is often reported in affected dogs as a “phantom scratching” (scratching movements aimed at the ears, shoulders or flank region) or diffuse unprovoked pain.
Gabapentin at a starting dose of 10 mg/kg BID-TID can be continued indefinitely and the dose can be increased as necessary; lethargy is sometimes observed. Gabapentin is used to treat neuropathic pain and can greatly improve comfort and reduce incidences of phantom scratching episodes. Omeprazole is dosed at 1 mg/kg once daily and is used to reduce the production of CSF, its mechanism of action is unknown. Some pharmacologists recommended alternate month dosing vs continuous dosing indefinitely. Corticosteroids can be helpful as pulse therapy at a low anti-inflammatory dose; they act to reduce pain and decrease the production of CSF. It is not recommended to keep these patients on continuous corticosteroid therapy indefinitely.
Tippy is currently on medical therapy as described above by the owner’s choice. She is doing well. Her owner might consider surgery if medical therapy becomes ineffective.