From arrest of function, from lesions, pressure, distal, but at times
central of lesion. Symptoms: Loss of function advancing to paralysis.
Muscle atrophy. Prognosis: in absence of incurable cause, is hopeful.
Union of divided ends, restoration of function. Treatment: time,
ligature of divided ends.
This is usually the result of arrest of function. It may be due to
transverse section of the nerve, as in surgical neurectomy when the
separated peripheral end of the nerve gradually wastes. It may come from
contused wounds implicating the nerve and causing destruction of its
substance. It may be from tumors or other neoplasms pressing on the
trunk of the nerve and preventing the passage of nerve currents. Or,
inflammatory effusion may press on the nerve, as happens often to the
crural in hæmoglobinuria. Or the pressure may come from enlarged
mediastinal glands, or even from the distended posterior aorta under
habitual violent exertion so as to permanently incapacitate and atrophy
the left recurrent laryngeal nerve as in chronic laryngeal paralysis
(roaring). Similar wasting occurs in other nerves under corresponding
conditions. Atrophy may, however, extend centrally from the peripheral
end of a nerve when it can no longer remain functionally active. We find
an example of this in the atrophy of the optic nerve up to the
commissure when the eyeball has been excised. A similar condition is
often seen in horses in which the integrity of the eye has been
completely destroyed in connection with recurring ophthalmia.
The _symptoms_ attendant on atrophy of a nerve are those of impaired
function gradually advancing to complete paralysis of motion or
sensation. In cases of a complete breach of continuity as in section or
severe traumatism the entire loss of function necessarily precedes the
atrophy. Again, when it comes from destructive changes in the coats and
media of the eye, and of the ganglionic cells of the retina, the atrophy
of the nerve trunk proceeds simultaneously with the lesions of the organ
of vision.
The _diagnosis_ will in many cases be easy as deduced from the traumatic
or surgical lesion. In other cases it may be made with certainty from
the complete muscular paralysis, wasting and degeneration of the muscles
supplied by the nerve, and by the history of the case (hæmoglobinuria in
atrophy of the triceps extensor cruris, roaring in atrophy of the
laryngeal muscles and recurrent nerve). In other cases, as in the eye,
we have the atrophy of the eyeball, the distortion or complete paralysis
of the iris, the opacity of the lens, or the exudation into the
vitreous, choroid and retina when these can still be observed.
_Prognosis_ will depend on the cause. With a nerve severed with a knife
or crushed in a part of its course and atrophied, without destructive
changes in the organs in which it is distributed, repair is possible and
to be expected in time.
_Treatment_ is expectant, yet inflammation must be subdued, tumors
removed, divided ends ligatured, etc.