Axonal Damage: What is it? Causes, Symptoms, Diagnosis, Therapy and Prognosis of A.Griguolo

Generality

Axonal damage is the most common and devastating type of traumatic brain injury.

Characterized, as the name suggests, by the breaking of the axons, the axonal damage recognizes in the traumas to the head that cause the violent shaking of the brain against the skull the main cause.

First, the victims of axonal damage lose consciousness for a few hours; subsequently, they could recover, manifesting a series of neurological symptoms related to the site of the brain lesions, or enter a state of coma or vegetative state, whose outcome is often fatal.

For the diagnosis of axonal damage, physicians must rely primarily on physical examination and history, as instrumental tests such as MRI or CT scan on the brain are unable to detect brain lesions.

At present, victims of axonal damage can only rely on treatments of a symptomatic nature, as there is still no medical or surgical therapy capable of eliminating lesions on axons.

What is the Asson?

The axon is the characteristic cellular extension of neurons, which is used by the latter to diffuse the nerve signals emitted by or destined for the brain .

Depending on the purpose of the neuron it belongs to, the axon may or may not be covered by a myelin sheath ; the axon provided with the myelin sheath is also called nerve fiber .

In neurons, the axon is added to the so-called body, which is the seat of the cell nucleus, and to the so-called dendrites, which are the antennas for receiving nerve signals from other neurons.

What is axonal damage?

Axonal damage is the most common and devastating type of brain injury following a head injury .

Also known as diffuse axonal damage or with the acronym DAI, axonal damage is characterized by damage to the axons of the cerebral white substance .

Axonal damage is a serious brain injury, which often leads to a state of irreversible coma (90% of coma cases due to axonal damage are irreversible) or in a vegetative state .

As the term "diffuse" suggests, axonal damage is not a circumscribed brain injury, but affects more areas of the brain.

Axonal damage can vary by gravity; depending on the extent of the brain injury, in fact, it may be mild, moderate or severe .

In general, the more the axonal damage is severe and the greater the probability that this cerebral injury leads to irreversible coma or in the vegetative state.

Did you know that ...

The abbreviation DAI used to indicate axonal damage is the English acronym of "Diffuse Axonal Injury", meaning "diffuse axonal damage".

Characteristics of Axonal Damage

The axonal damage is characterized by the cytoskeletal rupture of the axons of the cerebral white substance and by a series of secondary changes, such as: axonal transport disruption, axonal degeneration and stretching, microtubule misalignment present in the injured axons and unusual deposition of tau and APP (the accumulation of these proteins is often associated with suffering in the brain; in this regard one thinks, for example, of Alzheimer's disease);
The lesions to the white substance, observed in the presence of axonal damage, can vary in size from 1 to 15 millimeters;
Edema occurs in areas of brain injury that characterize axonal damage; this edema is an example of cerebral edema ;
The brain areas most prone to diffuse axonal damage are the brainstem, the corpus callosum, the cerebral lobes (in particular the frontal lobe and the temporal lobe), the so-called basal ganglia and the thalamus;
Histological studies have shown that axonal damage is not immediately following the trauma that causes it, but appears in the hours, if not even in the following days ; from the aforementioned studies, in fact, it emerged that the lesions of the axons are the consequence of a slow succession of biochemical alterations within the nerve cells involved.

Curiosity

The lesions observed in the presence of axonal damage arise from the anomalous presence of large quantities of calcium ions inside the nerve cells involved; scholars, in fact, have observed that these calcium ions trigger enzymes capable of damaging the mitochondria and the cytoskeleton of the neurons in which they are found, causing at the end of the entire lesion of the axons.

Causes

The Pathological Mechanism that produces Axonal Damage

Axonal damage is the result of traumatic shear forces, which occur when the head is subjected to acceleration or deceleration or to abrupt rotational movements; when the head is the subject of such episodes, in fact, there is a shaking of the brain against the internal walls of the skull, such as to cause the lesion of the axons, the interruption of axonal transport, etc.

The Causes of Axonal Damage

The most common causes of axonal damage are:

Motor vehicle accidents;
Accidental falls;
Sports accidents;
Physical aggression and abuse.

Curiosity

Lovers of motoring - especially Formula 1 - will surely have heard of axonal damage, on the occasion of the incident that took place during the race against Jules Bianchi on October 5, 2014, in Japan (Suzuka Grand Prix); following the reported brain injuries, the unfortunate pilot went into a coma and died after 9 months.

Symptoms and Complications

As a rule, axonal damage causes a loss of consciousness lasting a few hours (usually 6 or slightly more); after which, the patient enters a coma or a vegetative state, or recovers, though showing a series of symptoms that depend on the injured brain area.

Among the possible symptoms of axonal damage in a patient recovering from an unconscious state are:

Headache;
Dizziness, balance problems and coordination problems;
Cognitive deficits, such as memory problems, difficulty with concentration and organization, etc .;
Recurrent nausea and vomiting;
Permanent drowsiness and fatigue;

Insomnia;
Sudden changes in mood and sudden personality changes;
Disorientation and confusion;
Language problems (eg: difficulty speaking).

It is important to point out to the readers that the complete picture of the consequences of axonal damage is visible only a few days after the triggering trauma; this is connected to what was stated above, concerning the fact that the lesions against the axons are the result of a slow succession of biochemical alterations within the nerve cells involved.

Did you know that ...

The milder forms of axonal damage are examples of concussion (or cerebral concussion ).

Is Axonal Damage Permanent?

Axonal damage produces permanent injuries ; this means that the axons, once damaged, are irretrievably lost .

Therefore, victims of axonal damage are forced to live with all the problems that may arise from the present brain injuries.

Severity of Axonal Damage and Symptoms

The symptomatology of axonal damage is all the more articulated and debilitating, the more numerous and severe the brain lesions caused by trauma to the head.

Complications

If it is severe, axonal damage can lead to coma or vegetative state.

As previously reported, 90% of coma cases due to axonal damage are irreversible.

Those few people who manage to recover from a coma following an axonal injury are usually affected by profound cognitive deficits.

Diagnosis

Brain injuries produced by axonal damage are hardly visible on imaging examinations . This means that, for the diagnosis of axonal damage, doctors must rely mainly on objective examination and medical history, ie in-depth analysis of the symptoms exhibited by the patient and a questionnaire aimed at clearing the triggering factor of the symptomatology in progress.

When do you suspect an Axonal Damage?

In general, doctors consider the hypothesis of axonal damage, when:

The patient lost consciousness after a head injury (therefore, if there was a concussion);
The patient, upon awakening from unconsciousness, manifests cognitive deficits or other symptoms attributable to a brain injury;
The patient entered a coma or a vegetative state after a head injury followed by a loss of consciousness.

As previously stated, the complete symptomatic picture of an episode of axonal damage is visible after a few days of the triggering trauma.

Magnetic resonance and CT scan: why are they not very effective?

MRI and CT scans on the brain are not very effective in detecting axonal damage, because brain lesions are generally microscopic (and the aforementioned imaging tests can only detect macroscopic lesions).

Therapy

Currently, victims of axonal damage can only rely on treatments of a symptomatic nature, as there is still no medical or surgical therapy capable of eliminating lesions on axons.

Symptomatic therapy of axonal damage: what is it?

Symptomatic therapy of axonal damage includes:

The administration of corticosteroids, in order to reduce cerebral edema . Consequence of damaging events affecting the axons, cerebral edema requires immediate treatment, as its continuation can further damage the brain.
A specific rehabilitation program, in order to recover part of the lost cognitive functions and / or minimize the deficits acquired with brain injuries. The rehabilitation program varies from patient to patient, depending on the deficits present.
In a rehabilitation program for the victims an axonal damage, could include treatments such as, for example, logotherapy, physiotherapy and occupational therapy.
The rehabilitation program from axonal damage is much more likely to have positive implications, the more mild the brain lesions present.
The typical medical support offered to people in a coma or in a vegetative state . The use of this support obviously occurs when the victim of axonal damage has not been able to recover from the loss of consciousness.

Prognosis

Axonal damage is a serious neurological condition, which:

In the most fortunate ones, it involves a series of recoverable deficits partly through a precise rehabilitation program,

while

In the less fortunate, it leads to coma or vegetative state and subsequently to death (NB: the awakening from the coma is a very remote possibility).

In light of this, therefore, axonal damage is to be considered a condition with a non-positive prognosis, in milder cases, and decidedly inauspicious, in the most serious cases.

Readers are reminded that brain injuries resulting from axonal damage are permanent.