1. Lesions of Spinal Nerve Roots, Spinal nerves and Spinal Cord

2. I. Lesions in Dorsal and Ventral Roots of Spinal Nerves
Single dorsal root lesion cause partial loss of pain, temperature, proprioception, fine discriminatory touch and vibratory sense of ipsilateral dermatome innervated by the dorsal root in question. Such lesion rarely abolishes entirely the above modalities because the overlap of dorsal roots in innervating single dermatomes and the overlap of proximal processes of consecutive dorsal roots terminating in a single spinal cord segment.
Chronic degeneration of DRG cells due to neurosyphillis results in Tabes dorsalis (explained in the previous lecture).
Single ventral root lesion causes partial paralysis or paresis in one or more muscles. Because single muscles are innervated by more than one ventral root, paresis and hypotonia, rather than paralysis and absence of tone are likely to occur. Electromyographic testing may be required to detect symptoms.
Chronic degeneration of several anterior roots due to trauma or disease may result in paralysis or paresis with various degrees of hypotonia depending on severity of lesion. Poliomylitis due to chronic degeneration of spinal anterior horn motor neurons results in muscle paralysis, hypotonia and eventual atrophy of muscle mass. Fasciculations occur prior to muscle degeneration.

3. II. Lesions of Spinal Nerves
Lesions of single spinal nerves bring about combination of sensory and motor partial loses to single dermatomes and underlying muscles.
Lesions of several spinal nerves may bring about complete sensory loss of pain, temperature, proprioception, discriminatory touch and vibratory sense to one or more dermatomes depending how many nerves are involved in the lesion. Similarly paralysis of one or more muscles and diminished tone and reflexes (hypotonia and hyporeflexia, respectively) will be observed.
Compression and transection lesions yield different degrees of axonal Wallerian (i.e., anterograde) degeneration. Extent of regeneration of axons after such lesions is dependent on the milieu provided by the tissue.
In PNS regeneration of axons occurs approx. at a rate of 1mm/day.

6. III. Lesions of the Spinal Cord
Brown-Sequard Syndrome (hemisection of the cord, Lesion #1, Drawing I)
a. Loss of proprioception, two-point discrimination, vibratory sense and deep pressure over ipsilateral dermatomes at and below lesion level.
b. Ipsilateral spastic paralysis or paresis of muscles innervated by spinal segments below lesion level. Test for:
b1. Ankle clonus.
b2. Ipsilateral abdominal and cremasteric reflexes.
b3. Babinski sign.
c. Contralateral loss of pain and temperature in all dermatomes starting at one or two spinal segments below the lesion.
d. Some muscle wasting at lesion level.

7. III. Spinal Cord Lesions (Cont)
Syringomyelia (Lesion #2, Diagram I).
Cavitation of the cord in the region of the central canal. Usually cervical or upper thoracic spinal levels.
Destruction of the ant white commissure and crossing fibers of lat spinothalamic tracts (ALS) which results in bilateral loss of pain and temperature over one or more dermatomes at one segment below lesion level.
Cavitation may involve ventral horn resulting in paralysis or paresis of muscles innervated by ventral roots at lesion level.

8. III. Spinal Cord Lesions (Cont.)
Lesion of the lateral funiculus (Lesion #3, Diagram I).
Could be caused by meningioma pressing on lat funiculus or direct trauma to this area. Signs/symptoms include:
a. Ipsilateral spastic paralysis or paresis of all muscles below level of lesion.
b. Hyperactive deep tendon (myotatic) reflexes.
c. Ankle clonus.
d. Ipsilateral loss of cutaneous reflexes
e. Sympathetic dysfunction (lack of sweating, flushed skin due to vasodilation if lesion occurs between C1 and L2 spinal levels

9. III. Spinal Cord Lesions (Cont.)
Cauda Equina Syndrome
Usually trauma at the level of cauda equina (below LV2) involving dorsal and ventral roots of lumbar and sacral spinal nerves in the lumbar cistern.
Varying degrees of sensory and motor involvement in the lower limbs.
Pudental nerve (S2-4) involvement will result in bladder and rectal incontinences.
Erectile dysfunction due to involvement of parasympathetic vasodilator fibers in the pelvic splanchnics (nervi erigentes, S2-4).