The post-concussion syndrome (a.k.a., post-concussive disorder and post concussional disorder) has been controversial for decades. Without question, an acute post-concussion syndrome can be caused by the neurobiology of a mild traumatic brain injury (MTBI). Without question, a post-concussion syndrome can be worsened by psychological distress, social psychological factors (e.g., the nocebo effect, iatrogenesis, and misattributions), personality characteristics, and co-occurring conditions (e.g., chronic pain and insomnia). If due to the neurobiological effects of an injury to the brain, a post-concussion syndrome should be present in the first week post injury. Evaluating someone long after an injury, obtaining a cross-section of symptoms, and then attributing those symptoms to the remote injury can easily result in misdiagnosis.
The widely-cited estimate of 10–20% of patients suffering a long-term post-concussion syndrome is both confusing and incorrect. It is confusing because there is often an assumption that if a person reports symptoms long after an MTBI, that the symptoms are causally-related to the biological effects of the injury (by logical inference, the symptoms are related to damage to the structure or function of the brain). However, it is well established that these symptoms could be caused, maintained, or worsened by a large number of factors that are unrelated to traumatically-induced cellular damage. It is incorrect because the constellation of symptoms comprising the post-concussion syndrome likely occurs in far fewer than 10–20% of patients with remote MTBIs. The estimates of 10–20% have typically been based on selected, non-representative samples of the entire population of people who sustain an MTBI, and some of the literature has been misinterpreted as showing evidence of a syndrome when it in fact illustrates isolated, non-specific symptom reporting. It is emphasized in this chapter that the post-concussion syndrome is a non-specific cluster of symptoms that can be mimicked by a number of pre-existing or comorbid conditions. The biologically-based, traumatically-induced syndrome, theoretically, can also occur in tandem with these conditions.