Stratocyte's Guide To: Diagnosing Spinal Cord Disorders without an MRI

Obtaining a definitive diagnosis of spinal cord disorders, or myelopathy, is not always possible, even with an MRI! However, when you don't have the ability to refer your patient for advanced imaging, you are forced to collect as many clues as you can from your neurologic exam, history, and the diagnostic tools in your clinic. This article is intended to help you make the most of your detective work, enabling you to come up with the best plan possible for each patient that presents to you with a spinal cord neurolocalization.

1. In-depth Patient History?

A meticulous patient history is paramount, especially when diagnosing spinal cord diseases. This process involves more than just a cursory glance at the patient's past medical records. It requires a deep dive into the nuances of the pet’s current condition and its progression over time.

1.1 Acute vs. Chronic Onset:

Understanding whether the condition appeared suddenly (acute) or developed gradually over time (chronic) is critical. Acute onset conditions might suggest traumatic injuries, acute disc herniations, or vascular accidents. Chronic conditions, on the other hand, could indicate progressive degenerative diseases, chronic inflammatory processes, or slow-growing neoplasms.

1.2 Progression of Clinical Signs:

The trajectory of the clinical signs offers valuable insights. Are the clinical signs static, indicating a possible one-time event, or are they progressively worsening, suggesting a degenerative or neoplastic process? Some conditions are known for spontaneous improvement without treatment, such as vascular conditions (fibrocartilagenous embolism) or non-compressive spinal cord injuries (acute non-compressive nucleus pulposus extrusion).?

1.3 Environmental and Lifestyle Factors:

Gaining insight into the pet’s environment and lifestyle can also uncover potential risk factors or causes. For instance, a dog with a history of unsupervised outdoor activity should raise concern for traumatic fracture/luxation.?

1.4 Response to Previous Treatments:

Information about how the pet has responded to any previous treatments can also refine your differential list. For instance, if a pet has shown improvement with anti-inflammatory medications, this could suggest an inflammatory component to the spinal cord disease.

2. Perform a Complete Neurologic Exam and Determine the Neurolocalization

It is important to get in the habit of performing a complete neurologic exam for patients that present with any type of mobility issue. This assessment helps in differentiating between orthopedic and neurologic causes, localizing the neurological lesion, determining an accurate diagnosis and effectively managing the condition. Understanding the nuances of the neurologic exam allows veterinarians to discern subtle signs that could indicate more extensive or different pathologies than initially suspected.

2.1 Mentation Assessment

The patient’s level of consciousness, or mentation, is a key aspect of the neurological examination. In cases of myelopathy, which refers to pathology of the spinal cord, the mentation is typically unaffected. This means that:

• Patients with myelopathy usually maintain normal awareness and responsiveness. They might exhibit signs of anxiety or pain due to their spinal cord condition, but they will be alert and responsive.
• If a patient shows signs of being obtunded (decreased alertness), stuporous (only responsive to strong stimuli), or comatose (unresponsive), this usually indicates a problem within the brain rather than the spinal cord. Such signs necessitate a thorough examination for potential brain pathologies or systemic illness.

2.2 Cranial Nerve Examination

A comprehensive cranial nerve exam is crucial, as it helps differentiate between brain and spinal cord issues. In cases of myelopathy, the cranial nerves are typically unaffected, as these nerves emerge directly from the brain and brainstem, not the spinal cord. Therefore, a normal cranial nerve exam is expected in a patient with only a myelopathy.?

Horner Syndrome is a unique exception. It is often observed during cranial nerve exams but is not a direct result of cranial nerve dysfunction. Instead, it results from disruption of the sympathetic nerves that travel from the brain to the eye along a pathway that includes the cervical spinal cord. Horner Syndrome is characterized by signs such as miosis (constricted pupil), ptosis (drooping of the upper eyelid), enophthalmos (sunken appearance of the eye), and an elevated third eyelid. The presence of Horner Syndrome can point to pathology affecting the sympathetic pathway, which might include parts of the spinal cord, thus being indirectly related to a myelopathy.

2.3 Gait Analysis

Gait analysis is an essential aspect, particularly when assessing patients with potential spinal cord issues. It involves observing the animal's movement to identify abnormalities that could indicate either neurologic or orthopedic problems.

• Distinguishing Neurologic from Orthopedic Conditions: Orthopedic issues often manifest as lameness, characterized by a reluctance to use a limb due to pain or restricted range of motion. Neurologic conditions, however, may present as paresis (weakness) or ataxia (lack of coordination), indicating different underlying mechanisms and locations of pathology.
• Localizing the Lesion in the Spinal Cord: The type and pattern of gait abnormality can provide clues to the location of the spinal cord lesion. For instance, paresis in the hind limbs with normal front limb function could indicate a problem in the thoracolumbar spine (T3-L3), while issues in all four limbs might suggest a cervical spine (C1-C5) lesion.
• Determining Prognosis: Ultimately, the degree of neurologic deficits determines the degree of spinal cord compression, and ultimately the patient’s prognosis. The tracts on the outside of the spinal cord affect coordination and proprioception. As such, mild compression results in ataxia and decreased postural reactions. As you increase the compression (affecting deeper white matter tracts) you see increasing levels of weakness (paresis) to paralysis. Severe compression involving the grey matter at the center of the spinal cord can affect the patient’s sensation (ability to feel their feet caudal to the lesion). Countless studies on spinal cord injury in dogs have indicated that the loss of pain sensation (nociception) indicates a worse prognosis for most types of spinal cord injury. It is important that you establish whether or not your patient has voluntary motor during your gait analysis to help establish their prognosis.?

2.4 Postural Reaction Deficits and Reflexes

By systematically assessing postural reactions and reflexes, veterinarians can more accurately localize the spinal cord lesion. This localization is critical in determining the underlying cause of the neurologic deficit, guiding further diagnostics, and formulating a treatment plan.

Postural Reaction Deficits:

Postural reactions, including proprioceptive positioning, hopping, and extensor postural thrust, assess the animal's awareness of limb placement and movement. Deficits in these reactions can indicate a dysfunction in the sensory pathways that run through the spinal cord to the brain. For example, a lack of proprioceptive positioning in the hind limbs only suggests a problem in the thoracolumbar spinal cord (T3-S3).

Reflex Variations and Their Indications:

• C1-C5 Myelopathy: Myelopathies from C1 to C5 typically result in increased reflexes and tone in all four limbs (hyperreflexia and hypertonia). This is due to the interference of the upper motor neuron tracts that regulate limb movement and tone.
• C6-T2 Myelopathy: In this region, the pattern changes. There might be decreased reflexes and tone in the front legs (due to lower motor neuron involvement) and increased reflexes and tone in the back legs (upper motor neuron).
• T3-L3 Myelopathy: Myelopathies in this region often show normal reflexes in the front legs, with increased reflexes and tone in the back legs, indicating a lack of upper motor neurons regulation of the hind limbs.
• L4-S3 Myelopathy: Pathology here typically results in decreased reflexes and tone in the back legs only, reflecting lower motor neuron involvement in the hind limbs.

2.5 Nociception

Nociception, the sensory nervous system's response to certain harmful or potentially harmful stimuli, plays a crucial role in diagnosing and prognosticating spinal cord injuries, especially in cases where patients are unable to move their legs.

• Essence of Deep Pain Assessment: Assessing for deep pain, a type of nociception, is integral in determining the extent of a spinal cord injury. Deep pain sensation is mediated by specific pathways within the spinal cord that are more resistant to damage. The presence or absence of this sensation is a critical indicator of the spinal cord's functional integrity. Animals that retain deep pain sensation generally have a better prognosis for regaining mobility and function than those without it.
• Assessment Methodology: Deep pain sensation is tested by applying a stimulus that would typically cause discomfort. The key is to elicit a response that indicates the animal perceives the sensation as painful, not just reflexive movement. A positive response includes vocalizing, attempting to bite or move away, or a clear change in facial expression. Simply withdrawing the limb may be a spinal reflex and does not necessarily indicate pain perception.
• Importance of Conscious Recognition: The recognition of pain requires intact neural pathways from the site of the stimulus to the brain. This conscious recognition is what's crucial in assessing the severity and prognosis of spinal cord injuries.
• When to Assess Deep Pain: Any patient with voluntary motor will have sensation. Therefore, it is not necessary to assess deep pain in a patient that is walking! A thorough gait evaluation will help you determine if your patient has voluntary motor, enabling you to skip this potentially uncomfortable part of the assessment! If you cannot definitively determine whether your patient is able to move their legs, you should test for deep pain.

3. Spinal Palpation and Pain Response

Spinal palpation is a critical component of the neurological examination in veterinary patients. It provides valuable information about potential spinal issues and helps differentiate between various types of myelopathies, guiding both diagnostic and treatment pathways.?

• Purpose of Spinal Palpation: The primary aim of spinal palpation is to identify areas of pain or discomfort along the spine. This can be indicative of underlying pathologies. Different spinal cord diseases (myelopathies) can present with varying responses to palpation. The presence or absence of pain during palpation can guide the clinician in differentiating between these conditions.
• Technique and Observation: The technique involves gently palpating along the spine, from the cervical region down to the sacral area, applying mild pressure to assess for pain response, abnormal mobility, or any other irregularities. Positive pain responses, such as vocalization, tensing/flinching, or attempting to bite, can indicate a problem in the palpated area. No response or a neutral response might suggest conditions where pain isn't a primary feature.
• Differentiating Between Conditions:Type 1 Intervertebral Disc Disease (IVDD): This condition often results in pain during palpation. The herniated disc material puts pressure on the spinal cord and nerve roots, causing significant discomfort.Spinal Fractures/Luxations: Similar to IVDD, these are typically associated with pain on palpation due to the disruption of bone and potential impact on surrounding neural structures. Be extremely careful performing spinal palpation on any patient with a history suggestive of traumatic fracture/luxation.?Fibrocartilaginous Embolism (FCE): FCE often does not elicit a pain response during palpation. This condition involves the blockage of blood vessels in the spinal cord and doesn't directly affect the spine's structural integrity.Degenerative Myelopathy (DM): DM is another condition that does not produce pain on spinal palpation. Degenerative myelopathy is a progressive disease of the spinal cord, primarily affecting the white matter, without causing painful spinal lesions.

Tools other than MRI

• Myelography: Myelography involves the injection of a contrast dye into the space surrounding the spinal cord. This dye outlines the spinal cord on X-rays, providing enhanced visibility.
• CT Scans (Computed Tomography): CT scans offer better detail than standard radiographs, especially for bony structures. They provide cross-sectional images, giving a more comprehensive view of the spine.
• Radiographs (X-rays): Radiographs are one of the most accessible and commonly used imaging tools in veterinary practices. They are particularly effective in assessing bone structures, alignments, and certain types of spinal abnormalities. Radiographs are a good screening tool for patients with suspected fracture/luxation or vertebral tumors. However, radiographs alone can rarely diagnose intervertebral disc disease, cannot identify pathology of the spinal cord itself, and can miss about 25% of vertebral fractures and luxations.?

The Challenges of Diagnosing Without MRI

1. Uncertainty: Without MRI, some diagnoses may remain presumptive, based on the best interpretation of available information.
2. Management Decisions: Treatment plans may need to be more conservative or based on response to therapy, particularly when a definitive diagnosis is not possible.
3. Less detailed imaging like X-rays or CT scans can lead to presumptive diagnoses, where the exact nature or extent of the spinal issue is not fully confirmed.

In conclusion, diagnosing spinal cord disorders without access to advanced imaging like MRI or CT requires a comprehensive understanding of neurology, careful observation, and effective use of available diagnostics. To effectively diagnose spinal cord disorders without MRI or CT, a systematic approach is needed. This includes a thorough history, a complete neurologic exam, understanding the nature of myelopathy, and utilizing available diagnostics to refine the differential list.

By following the outlined strategies and consulting with virtual neurologists when needed, you can develop effective treatment plans and improve outcomes for your patients.