How many people have PCS after a concussion?
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Though no universally accepted definition of postconcussive syndrome exists, most of the literature defines the syndrome as the development of at least 3 of the following symptoms: headache, dizziness, fatigue, irritability, impaired memory and concentration, insomnia, and lowered tolerance for noise and light. One complication in diagnosis is that symptoms of PCS also occur in people who have no history of head injury, but who have other medical and psychological complaints. In one study 64% of people with TBI, 11% of those with brain injuries, and 7% of those with other injuries met the DSM-IV criteria for post-concussion syndrome. Many of these PCS sufferers were misdiagnosed as having other unrelated conditions due to commonality of symptoms. (see diagnosis, below).
Post-concussion syndrome
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Post-concussion syndrome, also known as postconcussive syndrome or PCS, is a set of symptoms that may continue for weeks, months, or a year or more after a concussion – a mild form of traumatic brain injury (TBI). The rates of PCS vary, but most studies report that about 15% of individuals with a history of a single concussion develop persistent symptoms associated with the injury. A diagnosis may be made when symptoms resulting from concussion last for more than three months after the injury. Loss of consciousness is not required for a diagnosis of concussion or post-concussion syndrome.
Post-concussion syndrome
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About 10% of people with PCS develop sensitivity to light or noise, about 5% experience a decreased sense of taste or smell, and about 14% report blurred vision. People may also have double vision or ringing in the ears, also called tinnitus. PCS may cause insomnia, fatigue, or other problems with sleep.
Post-concussion syndrome
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The prognosis for PCS is generally considered positive, with total resolution of symptoms in many, but not all, cases. For 50% of people, 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, but evidence indicates that many cases are completely resolved within 6 months. The majority of symptoms are largely gone in about half of people with concussion one month after the injury, and about two thirds of people with minor head trauma are nearly symptom-free within three months. Persistent, often severe headaches are the longest lingering symptom in most cases and are the most likely symptom to never fully resolve. It is frequently stated in the literature and considered to be common knowledge that 15–30% of people with PCS have not recovered by a year after the injury, but this estimate is imprecise because it is based on studies of people admitted to a hospital, the methodologies of which have been criticized. In approximately 15% of people, symptoms may persist for years or be permanent. If symptoms are not resolved by one year, they are likely to be permanent, though improvements may occur after even two or three years, or may suddenly occur after a long time without much improvement.
Older people and those who have previously suffered another head injury are likely to take longer to recover.
Post-concussion syndrome
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The condition is associated with a wide range of symptoms: physical, such as headache; cognitive, such as difficulty concentrating; and emotional and behavioral, such as irritability. Many of the symptoms associated with PCS are common or may be exacerbated by other disorders, so there is considerable risk of misdiagnosis. Headaches that occur after a concussion may feel like migraine headaches or tension-type headaches. Most headaches are tension-type headaches, which may be associated with a neck injury that occurred at the same time of the head injury.
A common condition associated with PCS is headache. While most people have headaches of the same type they experienced before the injury, people diagnosed with PCS often report more frequent or longer-lasting headaches. Between 30% and 90% of people treated for PCS report having more frequent headaches and between 8% and 32% still report them a year after the injury.
Post-concussion syndrome
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It is not known exactly how common PCS is. Estimates of the prevalence at 3 months post-injury are between 24 and 84%, a variation possibly caused by different populations or study methodologies. The estimated incidence of PPCS (persistent postconcussive syndrome) is around 10% of mTBI cases. 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, and, consequently, of developing PCS.
Post-concussion syndrome
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The ICD-10 established a set of diagnostic criteria for PCS in 1992. In order to meet these criteria, a patient has had a head injury "usually sufficiently severe to result in loss of consciousness" and then develop at least three of the eight symptoms marked with a check mark in the table at right under "ICD-10" within four weeks.
About 38% of people who suffer a head injury with symptoms of concussion and no radiological evidence of brain lesions meet these criteria. In addition to these symptoms, people that meet the ICD-10 criteria for PCS may fear that they will have permanent brain damage, which may worsen the original symptoms. Preoccupation with the injury may be accompanied by the assumption of a "sick role" and hypochondriasis. The criteria focus on subjective symptoms and mention that neuropsychological evidence of significant impairment is not present. With their focus on psychological factors, the ICD-10 criteria support the idea that the cause of PCS is functional. Like the ICD-10, the ICD-9-CM defines PCS in terms of subjective symptoms and discusses the greater frequency of PCS in people with histories of mental disorders or a financial incentive for a diagnosis.
Post-concussion syndrome
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Conventional neuroimaging studies of the brain following a concussion are typically normal. However, studies have found some subtle physiological changes associated with PCS using more novel imaging modalities. Studies using positron emission tomography have linked PCS to a reduction in glucose use by the brain. Changes in cerebral blood flow have also been observed as long as three years after a concussion in studies using single photon emission computed tomography (SPECT). At least one study with functional magnetic resonance imaging (fMRI) has shown differences in brain function during tasks involving memory after mild traumatic brain injury (mTBI) although they were not examining PCS specifically. Additional studies have shown, using various MRI techniques (such as Diffuse Tensor Imaging (DTI) MRI), that individuals with PCS have various abnormalities in their brain structure. Similar findings have recently been reported in soldiers with blast-induced mTBI/PCS.
Post-concussion syndrome
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Post-concussion syndrome (PCS), is a set of symptoms that a person may experience for weeks, months, or occasionally years after a concussion with a prevalence rate of 38–80% in mild traumatic brain injuries, it may also occur in moderate and severe cases of traumatic brain injury. A diagnosis may be made when symptoms resulting from concussion, depending on criteria, last for more than three to six months after the injury, in which case it is termed persistent postconcussive syndrome (PPCS). In a study of the prevalence of post concussion syndrome symptoms in patients with depression utilizing the British Columbia Postconcussion Symptom Inventory: "Approximately 9 out of 10 patients with depression met liberal self-report criteria for a postconcussion syndrome and more than 5 out of 10 met conservative criteria for the diagnosis." These self reported rates were significantly higher than those obtained in a scheduled clinical interview. Normal controls have exhibited symptoms of PCS as well as those seeking psychological services. There is considerable debate over the diagnosis of PCS in part because of the medico-legal and thus monetary ramifications of receiving the diagnosis.
Differential diagnoses of depression
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Not all people with PCS have abnormalities on imaging, however, and abnormalities found in studies such as fMRI, PET, and SPECT could result from other comorbid conditions such as depression, chronic pain, or post-traumatic stress disorder (PTSD). 
Proponents of the view that PCS has a physiological basis point to findings that children demonstrate deficits on standardized tests of cognitive function following a mild TBI. A few studies have shown that people with PCS score lower than controls on neuropsychological tests that measure attention, verbal learning, reasoning, and information processing, but issues related to effort and secondary gain can not be ruled out as contributing to these differences. Recovery as measured by scores on cognitive tests frequently do not correlate with resolution of symptoms; individuals diagnosed with PCS may still report subjective symptoms after their performance on tests of cognitive functioning have returned to normal. Another study found that although children with PCS had poorer scores on tests of cognitive functioning after the injury, they also had poorer behavioral adjustment before the injury than children with no persistent symptoms; these findings support the idea that PCS may result from a combination of factors such as brain dysfunction resulting from head injury and preexisting psychological or social problems. Different symptoms may be predicted by different factors; for example, one study found that cognitive and physical symptoms were not predicted by the manner in which parents and family members coped with the injury and adjusted to its effects, but psychological and behavioral symptoms were.
Post-concussion syndrome
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The symptoms that occur after a concussion have been described in various reports and writings for hundreds of years. The idea that this set of symptoms forms a distinct entity began to attain greater recognition in the latter part of the 19th century. John Erichsen, a surgeon from London, played an important role in developing the study of PCS. The controversy surrounding the cause of PCS began in 1866 when Erichsen published a paper about persisting symptoms after sustaining mild head trauma. He suggested that the condition was due to "molecular disarrangement" to the spine. The condition was originally called "railroad spine" because most of the injuries studied had happened to railroad workers. While some of his contemporaries agreed that the syndrome had an organic basis, others attributed the symptoms to psychological factors or to outright feigning. In 1879, the idea that a physical problem was responsible for the symptoms was challenged by Rigler, who suggested that the cause of the persisting symptoms was actually "compensation neurosis": the railroad's practice of compensating workers who had been injured was bringing about the complaints. Later, the idea that hysteria was responsible for the symptoms after a mild head injury was suggested by Charcot. Controversy about the syndrome continued through the 20th century. During World War I many soldiers suffered from puzzling symptoms after being close to a detonation but without any evidence of a head wound. The illness was called "shell shock," and a psychological explanation was eventually favoured. By 1934 the current concept of PCS had replaced ideas of hysteria as the cause of post-concussion symptoms. British authorities banned the term "shell shock" during World War II to avoid an epidemic of cases, and the term "posttrauma concussion state" was coined in 1939 to describe "disturbance of consciousness with no immediate or obvious pathologic change in the brain". The term "postconcussion syndrome" was in use by 1941.
Post-concussion syndrome
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In the past, the term PCS was also used to refer to immediate physical symptoms or post-concussive symptoms following a minor TBI or concussion. The severity of these symptoms typically decreases rapidly. In addition, the nature of the symptoms may change over time: acute symptoms are most commonly of a physical nature, while persisting symptoms tend to be predominantly psychological. Symptoms such as noise sensitivity, problems with concentration and memory, irritability, depression, and anxiety may be called 'late symptoms' because they generally do not occur immediately after the injury, but rather in the days or weeks after the injury. Nausea and drowsiness commonly occur acutely following concussion. Headache and dizziness occur immediately after the injury, but also can be long lasting.
Post-concussion syndrome
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The existence of PCS in children is controversial. 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 known to result from moderate and severe head trauma). On the other hand, children's brains may be more vulnerable to the injury, since they are still developing and have fewer skills that can compensate for deficits. Clinical research has found higher rates of post-concussion symptoms in children with TBI than in those with injuries to other parts of the body, and that the symptoms are more common in anxious children. Symptoms in children are similar to those in adults, but children exhibit fewer of them. Evidence from clinical studies found that high school-aged athletes had slower recoveries from concussion as measured by neuropsychological tests than college-aged ones and adults. PCS is rare in young children.
Post-concussion syndrome