Post-concussion syndrome
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# Overview
Post-concussion syndrome, also known as postconcussive syndrome or PCS, is a set of symptoms that a person may experience for weeks, months, or even years after a concussion, a mild form of traumatic brain injury (TBI).   As many as 50% of patients who have experienced concussion have PCS,  but the prevalence is not well known and varies based on the definition of the syndrome and the length of time after which it is diagnosed.
PCS is the most common entity to be diagnosed after TBI. A diagnosis of PCS may be made in patients who have symptoms resulting from concussion for more than three months after the injury, or it may be made in patients with symptoms starting within a week of trauma.  In late, persistent, or prolonged PCS (PPCS), symptoms last for over six months, or by other standards, three. Most cases of PCS go away on their own in time.
PCS may also occur in sufferers of moderate and severe TBI.
It is not known what causes PCS symptoms to occur and persist or why some patients who suffer a mild traumatic brain injury (mTBI) develop PCS while others do not.  It is commonly believed that physiological and psychological factors before, during, and after the injury all take part in the development of PCS.
The name "post-concussive syndrome" was first coined by S. H. Auerbach. The nature of the syndrome and the diagnosis itself have long been the subject of intense debate.

# Signs and symptoms
People who have had concussions may experience physical, mental, or emotional symptoms, which can appear immediately or weeks to months after the initial injury. As time goes on, symptoms become predominantly psychological ones, such as anxiety, rather than the physical symptoms such as headache seen earlier on.
Physical symptoms can include:
- headache, the main symptom, frequently persists for up to two weeks, and may last months
- dizziness, which occurs in 60% of cases, is the other most common symptom.
- impaired balance
- nausea and/or vomiting
- fatigue or sleepiness
- problems with sleep
- decreased libido
- sensitivity to noise or light
- ringing in the ears
- double or blurred vision
- loss of hearing, which occurs in 20% of cases
- decreased sense of taste or smell
Emotional  symptoms may include:
- irritability
- anxiety
- restlessness
- depression
- lack of emotion
- emotional lability or mood swings
- lack of ability to tolerate stress or alcohol
- aggression
Cognitive  or mental symptoms can include:
- amnesia or difficulty remembering things
- confusion or impaired cognition
- impaired judgment
- slowed cognitive processing
- difficulty with abstract thinking
- problems with attention
- decrease in work performance
- decrease in social skills
Severity of symptoms slowly lessens as time goes on. Problems with memory and attention are the longest-lasting cognitive symptoms.

# Controversy
Doubt exists about the validity of PCS as a diagnosis.  No definition of the syndrome is accepted by all health professionals. Though people have known about the syndrome for hundreds of years, it is not known to exactly what degree the symptoms are due to microscopic damage to the brain or to other factors, for example psychological ones.  This question has been heavily debated for many years.  It is widely believed that physiological factors are responsible for early symptoms that occur after mild head trauma, whereas symptoms that occur later are due to psychological factors.
It has been shown that psychological factors play an important role in post-concussion symptoms.  However,  structural damage does occur after some concussions.  Experiments have shown that physiological damage such as apoptosis occurs after minor TBI such as concussion.   According to the National Institute for Health and Clinical Excellence definition, concussion may involve damage to neurons.
Symptoms may be psychogenic; that is, they may be a result of the patient's psychological or emotional, rather than physiological, state. Symptoms may be due to psychological or social factors, such as patients' expectations that they will experience these symptoms.
Malingering may also occur, especially in cases involving litigation or other potential gain for the patient.  PCS is rare in young children, and in countries where lawsuits are less common, PCS symptoms are also less common.  Some evidence suggests that symptoms are worse in patients involved in litigation or compensation claims; however the stress from these activities could worsen post-concussion symptoms. Other studies have failed to show a link between litigation and symptom severity or duration, and symptoms do not necessarily go away when legal matters come to a close.  Neuropsychological tests exist to detect malingering.
PCS is more prevalent in patients who had psychiatric symptoms such as clinical depression or anxiety before the injury.
Cognitive and affective symptoms that occur following a traumatic injury may be attributed to MTBI but may in fact be due to another factor such as post-traumatic stress distorder.
Another reason that PCS is a controversial diagnosis is that the syndrome may be diagnosed in a patient who is actually healthy, because symptoms of post-concussion syndrome occur spontaneously in the general population of healthy, young and middle-aged adults at a fairly high rate. In one study, 80% of healthy, uninjured people reported having 3 or more symptoms like those found after concussion.  In addition, symptoms of PCS may be caused by other conditions.  For example, depression, which is highly common in persistent PCS, can worsen other PCS symptoms, such as headaches and problems with concentration, memory, and sleep.
Because symptoms are so varied and many can be associated with a large number of other conditions, doubt exists about whether the term "syndrome" is appropriate for the constellation of symptoms found after concussion. The fact that the persistence of one symptom is not necessarily linked to the persistence of another has similarly led to doubt about whether "syndrome" is the appropriate term.

# Diagnosis
The ICD-10 first proposed a set of diagnostic criteria for PCS in 1992. In order to meet these criteria, a patient must have had a head injury and develop at least three of the following eight symptoms within four weeks:
- headache
- dizziness
- fatigue
- irritability
- sleep problems
- problems with concentration
- problems with memory
- reduced ability to tolerate stress, emotion, or consumption of alcohol
About 38% of patients who suffer a head injury with  symptoms of concussion and no radiological evidence of brain lesions meet these criteria.  In addition to these symptoms, sufferers of PCS may fear that they will have permanent brain damage, which may worsen the original symptoms. In addition to becoming preoccupied with the injury, they assume a "sick role"  and exhibit hypochondriasis.
The DSM-IV lists criteria for diagnosis of postconcussional disorder in patients who suffered a concussion after a head trauma with memory or attention problems and at least three of the following:
- headache
- dizziness
- fatigue
- problems with sleep
- irritability
- changes in affect
- change in personality
- apathy
These symptoms must be present for 3 months after the injury and must have been absent or less severe before the injury. In addition, the patient must experience social problems as a result, and must not meet criteria for another disorder that explains the symptoms better.
After a concussion, the patient may be tested to determine his or her level of cognitive functioning. A test called the Rivermead Postconcussion Symptoms Questionnaire exists to measure the severity of the patient's symptoms. Loss of consciousness during the injury is not necessary for a diagnosis of PCS.

## Differential diagnosis
Because of the similarities to other conditions, such as depression, there is a risk that doctors may misdiagnose PCS.  For example, depression may be mistaken for PCS.  Traumatic brain injury may cause damage to the hypothalamus or the pituitary gland.  Deficiencies of pituitary hormones (hypopituitarism) can cause similar symptoms to post-concussion syndrome and should thus be considered as a cause for symptoms before diagnosing post-concussion syndrome. Hypopituitarism can be treated by replacing any hormone deficiencies.

## Diagnosis in children
It is possible that children's brains have enough plasticity that they are not affected by long-term consequences of concussion (though such consequences are well known to result from moderate and severe head trauma).  Clinical research has found higher rates of PCS in children with TBI than in those with injuries to other parts of the body, but that PCS was more common in anxious children. Symptoms in children are like those in adults, but children exhibit fewer symptoms than do their adult counterparts.  The development of PCS may be due to a combination of factors such as adjustment after the injury, preexisting vulnerabilities, and brain dysfunction.

# Treatment
There is no scientifically established treatment for PCS, so the syndrome is usually not treated. Treatment focuses on the specific symptoms involved. Sufferers can take pain relievers for headaches and medicine to relieve depression, dizziness or nausea.  Rest is also advised but is only somewhat effective.
About 40% of PCS patients are referred to psychological consultation. Psychological treatment has been shown to reduce problems.  When patients have ongoing disabilities, they are treated with therapy to help them function at work, socially, or in other contexts. Patients are aided in gradually returning to work and other preinjury activities as symptoms permit. Since stress exacerbates post-concussion symptoms, and vice versa, an important part of treatment is letting the patient know that symptoms are normal and helping the patient deal with impairments.  Education about symptoms and their usual time course is a part of psychological therapy, and is most effective when provided early after the injury.  Cognitive behavioral therapy may also be recommended, and may help prevent persistence of symptoms from iatrogenic causes, e.g. when sufferers manifest symptoms because they are led to expect to by health care providers.
In situations such as motor vehicle accidents or following an attack, the post-concussion syndrome may be accompanied by post-traumatic stress disorder, or PTSD. This is important to recognize and treat in its own right.  Sufferers of PTSD, depression, and anxiety can be treated with medication and psychotherapy.
No pharmacological treatments exist especially for PCS, but doctors may prescribe the same medications for symptoms that also occur in other conditions; for example, antidepressants are used for the depression that frequently follows mTBI.   Side effects of medications may affect people suffering the consequences of mTBI more severely than they do others, and thus it is recommended that medications be avoided where possible.  There may be a benefit to avoiding narcotic medications.

# Prognosis
For most patients, post concussion symptoms go away within a few days to several weeks after the original injury occurs. In others, symptoms may remain for three to six months.  Symptoms are largely gone in about half of people with concussion by one month after the injury and about two thirds by three months.  An estimated 15 to 20% of concussion patients have symptoms lasting months or years.  In a small percentage of patients, symptoms may persist for years or may be permanent.  If symptoms are not resolved by one year, they are likely to be permanent (though some people report improvements after even 2 or 3 years' time).  However, the prognosis for PCS is generally considered excellent, with total resolution of symptoms in the large majority of cases.  Patients may recover suddenly after a long time without much improvement.
Older patients and those who have previously suffered another head injury are likely take longer to recover.
If a patient receives another blow to the head after a concussion but before concussion symptoms have gone away, there is a slight risk that he or she will develop the very rare but deadly second-impact syndrome (SIS).  In SIS, the brain rapidly swells, greatly increasing intracranial pressure.

# Epidemiology
PCS is commonly more severe in women than in men, and women are at a greater risk for the diagnosis.  People over the age of 55 are more likely to have long-lasting symptoms. Since PCS by definition only exists in people who have suffered a head injury, demographics and risk factors are similar to those for head injury; for example, young adults are at higher risk than others for receiving head injury. Some studies have questioned the validity of a diagnosis of PCS in children after finding differences in PCS symptoms between head injured and control groups of children not to be statistically significant.  Others have found the incidence of PCS to be quite similar between children and adults.
Having headache, nausea, or dizziness immediately after concussion may increase a person's risk for a later PCS diagnosis.
It is commonly believed that 15% of patients still suffer PCS 12 months after the injury, but this figure may be an overestimate because it is based on people admitted to a hospital. It has not been conclusively shown that an uncomplicated concussion ever leads to permanent neurological symptoms.