Differences between spinal cord and brain lesions
A spinal cord lesion is considered an exception to the general logic of topographic diagnostics. A key sign is the absence of symptoms on the face: cranial nerves are not affected, there are no oculomotor disorders, no central or peripheral paresis of facial muscles, and no bulbar or pseudobulbar syndromes.
Clinical manifestations are limited to the limbs and trunk. If a patient has central paresis exclusively in the limbs without involvement of cranial musculature, brain and peripheral nervous system lesions are ruled out, and the diagnostic search focuses on the spinal cord.
Lesions of the gray and white matter of the spinal cord
Two fundamentally different types of lesions are distinguished within the cross-section of the spinal cord.
- Gray matter — the segmental apparatus is affected. A lesion of the anterior horns produces peripheral paresis at the segmental level with extinction of corresponding reflexes and the appearance of fasciculations. The posterior horns cause segmental dissociated sensory disorders.
- White matter — the funiculi and the pathways running within them are affected: the pyramidal tract, spinothalamic tracts (pain and temperature sensitivity), posterior columns (deep sensitivity). Conductor-type disorders arise below the level of the lesion.
Rule of two segments and lateralization
When formulating a clinical problem, the level of sensory disturbance on the skin is frequently indicated. A simple rule is applied to transition from the clinical level to the anatomical localization of the lesion.
- Determine the side of the clinical disorders. The lesion of the spinothalamic tract is localized on the opposite side to the superficial sensory disturbance.
- Raise the level by two segments upward relative to the dermatomal level of clinical manifestations (this is due to the peculiarities of fiber crossing in the anterior white commissure).
Example: in case of loss of pain and temperature sensitivity on the right at the Th12 level, the topical lesion is located on the left at the Th10 level.
Peripheral nervous system: general signs
A lesion of the peripheral nervous system is characterized by a combination of peripheral paresis (atonia, areflexia, atrophy, fasciculations) and sensory disorders following one of the types:
- mononeuropathic — in the innervation zone of a single nerve;
- polyneuropathic — in a "glove and stocking" pattern;
- radicular — along dermatomes, in the form of "stripes" (lampasses).
The appearance of fasciculations indicates involvement of the motor neurons of the anterior horns or the nerve root.
Lesions of the anterior and posterior roots
Two variants of lesions with fundamentally different clinical presentations are distinguished at the root level.
- Posterior root (sensory): shooting radicular pains, loss of corresponding segmental reflexes, impairment of all types of sensitivity in the dermatome zone in a "stripe" pattern. The clinical picture resembles radicular syndrome in intervertebral disc pathology.
- Anterior root (motor): peripheral paresis of indicator muscles innervated by the given segment. Pain syndrome is not typical, and sensitivity is preserved.
Algorithm of topographic diagnostics
The generalized logic of analyzing neurological deficit is built sequentially:
- Assess the presence of cranial symptomatology. Its presence indicates the brain (hemispheres or brainstem).
- In the absence of cranial signs and the presence of central paresis in the limbs, consider the spinal cord.
- Clarify whether the gray or white matter is affected: segmental disorders versus conduction disorders.
- Determine the side and level taking into account decussations and the rule of two segments.
- In case of peripheral paresis with sensory disorders of mononeuropathic, polyneuropathic, or radicular type, diagnose a PNS lesion, differentiating between the anterior and posterior roots.
Key points
- Spinal cord lesions are not accompanied by cranial nerve or facial symptoms.
- Gray matter causes segmental disorders, while white matter causes conduction disorders.
- In case of superficial sensory impairment, the lesion is localized on the opposite side and two segments above the clinical level.
- Signs of a PNS lesion are peripheral paresis and sensory disturbance of mono-, poly-, or radicular type.
- Fasciculations indicate a lesion of the anterior horns or anterior roots.
- Posterior root: shooting pains, loss of reflexes, sensory disturbances in a "stripe" pattern.
- Anterior root: peripheral paresis of indicator muscles without pain.
- Topical diagnosis is built according to the scheme "side → level → gray/white matter → root or nerve".