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Many concepts
in this page, have been adapted from J. Woessner: A conceptual model
of pain, Practical Pain Management, Volume 2, Issue 5.
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| Modified from “Pain
Transmission Pathways”, Endo Pharmaceuticals Inc. |
A. Nociceptive pain
Normal pain perception (Nociceptive pain) results from stimulation
of intact peripheral nerve fibers (pain sensors) in the vulva. Mechanical
(trauma), thermal (heat or cold), or chemical (caustic substances)
stimulation of the vulva, gives a good and normal information and
warning to the brain, that the vulvo-vaginal area is damaged or
about to be damaged.
B. Types of peripheral nerve fibers
There are three types of fibers that carry pain signals from the
vulva to the brain: A-beta, A-delta and C-fibers. The first two
are well evolved, myelinated (insulated) fibers that rapidly carry,
well defined sharp, lancinating pain signals to the cortical (upper)
regions of the brain. The C-fibers are relatively primitive, unmyelinated
fibers that slowly conduct ill defined aching and burning sensations
to the subcortical region of the brain.
| CHARACTERISTICS OF PERIPHERAL
NERVE FIBER TYPES |
| Class |
Stimuli/function |
Perception |
Velocity: m/sec |
Diameter: micron |
Myelination |
| A-alpha fibers |
Motor contraction Efferent transmission |
None |
30-85 |
12-22 |
+ + + |
| A-beta fibers |
Vibration and pressure Afferent transmission |
Vibration and pressure |
30-70 |
5-12 |
+ + + |
| A-delta fibers |
Cold sensation and pain
Fast pain and localized touch
Afferent transmission
|
Cold sensation and pain
localized touch
|
5-25 |
1-4 |
+ + |
| C fibers |
Hot sensation and pain Slow pain and generalized touch Afferent
transmission |
Hot sensation and pain
generalized touch |
0.7-2.0 |
0.3-1.3 |
- |
C. Neuropathic pain
The pudendal, genitofemoral, and ilioinguinal nerves are the main
nerves serving the vulvo-vaginal area. Any trauma or damage to the
vulvo-vaginal area can traumatize the nerves themselves. Damage
to the neural transmission can manifest itself analogous to “static”
in radio transmissions. This neural “static” results
in the spontaneous firing by the C-fibers of the vulva, and is perceived
as a continuous dull, aching, or burning pain. Neuropathic pain
results therefore, from damaged and malfunctioning nerve fibers.
D. Therapy of neuropathic vulvo-vaginal
pain
Neuropathic vulvo-vaginal pain can be successfully treated with
Gabapentin (Neurontin) an anti-convulsant, 300-1200 mg PO tid, or
Amitriptyline (Elavil) a tricyclic anti-depressant, 0.5-2 mg/kg
PO qhs. Both of these drugs seem to help reduce the “static”
spontaneous firing of the C-fibers. If the pudendal neuralgia is
associated with levator ani myalgia, a bilateral pudendal block
will help relieve the painful spasm.
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