Etiology.—Cold is a common cause, involving especially the facial and sciatic nerves, and gives rise to the so-called rheumatic neuritis.
Trauma is perhaps the most frequent cause and may be due to stretching or tearing that so often accompanies fractures and dislocations, or it may be due to severe muscular exertion, or to wounds, contusions, or hypodermic injections, or the continued strain on certain muscles, as seen in professional palsies.
The various toxins found in the infectious diseases may act upon a single nerve, though usually they produce multiple neuritis. A nerve may be involved by an extension of an inflammation from some neighboring part.
Pathology.—The inflammation may be confined to the perineurium, the nerve-sheath, or extend to the deeper tissues—interstitial—or involve the axis cylinder—parenchymatous. Where the sheath is involved, the nerve becomes swollen, hyperemic, and infiltrated with leukocytes.
Where the axis cylinder is affected—parenchymatous neuritis—degenerative changes take place, the nuclei of the nerve-cells consisting of oily-looking globules, a fatty degeneration.
Symptoms.—These depend somewhat upon the functions of the nerve involved. If a sensory nerve be the seat of the lesion, the pain is intense, and is of a burning, boring, aching, or shooting character. There is also tenderness on pressure, or when the muscles are moved. Although exquisitely painful, tactile sensation is materially lessened.
If a motor nerve be affected, there will be twitching of the muscles, supplied by the nerve, and if it assumes a chronic character, there will be paralysis and atrophy of the muscles.
Frequently both sensory and motor nerves are involved with a combination of symptoms.
Where the disease assumes a chronic form, trophic changes are manifest. There is a loss of faradic irritability, the skin becomes glossy and edematous, the nails become impaired, localized sweatings may arise, the surface temperature is sometimes increased, and there may be effusion into the joints.
Diagnosis.—We diagnose neuritis from neuralgia, the only lesion with which it might be mistaken, by the continuous character of the pain, which is increased by pressure. Altered sensation would also suggest neuritis.
Prognosis.—This is favorable in mild cases, the disease yielding within ten days or two weeks. If it assumes a chronic form, it may persist for months or years. If the continuity of the nerve be preserved, recovery will take place.
Treatment.—The part should have rest and support; where the pain is intense, a hypodermic of morphia may be required to relieve the pain. Hot applications generally afford more relief than cold ones. After tenderness disappears, much benefit will be derived from galvanism and massage.
When due to cold—rheumatic neuritis—the antirheumatics will be found efficient. Bryonia, apocynum, macrotys, rhamnus Californica, and the salicylates will be among the best.
If the skin is red, glossy, and edematous, apocynum is a good remedy. Jaborandi sometimes gives marked relief.