Post-concussion syndrome (PCS) occurs when symptoms resulting from a concussion, also known as a mild traumatic brain injury (mTBI), persist beyond the expected timeframe of recovery, although there is disagreement among the literature as to the exact duration of symptoms necessary for this diagnosis (many sources state a duration of one month). 
The WHO International Classification of Diseases, 10th Revision (ICD-10) defines PCS as: 
- History of head trauma with loss of consciousness preceding symptom onset by a maximum of 4 weeks.
- Symptoms in 3 or more of the following symptom categories:
- Headache, dizziness, malaise, fatigue, altered noise tolerance
- Irritability, depression, anxiety, emotional lability
- Subjective concentration, memory, or intellectual difficulties without neuropsychological evidence of marked impairment
- Reduced alcohol tolerance
- Preoccupation with above symptoms and fear of brain damage with hypochondriacal concern and adoption of sick role
The DSM-IV defines PCS as: 
- A history of head trauma that has caused significant cerebral concussion. Note: The manifestations of concussion include loss of consciousness, posttraumatic amnesia, and less commonly, the post-traumatic onset of seizures. The specific method of defining this criterion needs to be established by further research.
- Evidence from neuropsychological testing or quantified cognitive assessment of difficulty in attention (concentrating, shifting focus of attention, performing simultaneous cognitive tasks) or memory (learning or recall of information).
- Three (or more) of the following occur shortly after the trauma and last at least 3 months:
- Becoming fatigued easily
- Disordered sleep
- Vertigo or dizziness
- Irritability or aggression on little or no provocation
- Anxiety, depression, or affective instability
- Changes in personality (e.g., social or sexual inappropriateness)
- Apathy or lack of spontaneity
- The symptoms in criteria B and C have their onset following head trauma or else represent a substantial worsening of pre-existing symptoms.
- The disturbance causes significant impairment in social or occupational functioning and represents a significant decline from a previous level of functioning. In school-age children, the impairment may be manifested by a significant worsening in school or academic performance dating from the trauma.
- The symptoms do not meet criteria for Dementia Due to Head Trauma and are not better accounted for by another mental disorder (e.g. Amnestic Disorder Due to Head Trauma, Personality Change Due to Head Trauma).
Studies suggest that 21-59% of paediatric patients (age 18 and younger) who experience concussion will develop persistent symptoms lasting longer than one month.
Some of the most common and debilitating symptoms experienced by patients after a concussion are those involving dysfunction of the oculomotor and vestibular systems.
Symptoms of Vestibulo-ocular dysfunction (VOD) may include, but are not limited to:
- Motion sensitivity
- Postural or gait imbalances
- Blurred vision
- Gaze instability
Risk Factors for Developing Post-Concussion Syndrome
A study comparing children and adolescents with sport-related concussions who had short recovery times (30 days or less) to those who developed post-concussion syndrome, found that PCS was more likely to occur in:
- Patients who reported amnesia at the time of concussion
- Patients diagnosed with Vestibulo-ocular dysfunction (double the average recovery time as those without VOD, and 4X higher odds of developing PCS)
- Patients with higher PCSS scores (concussion severity indicator)
Other Risk Factors identified in the literature: Age, gender (female), previous concussion, previous migraine, loss of consciousness at time of injury.
Vestibulo-ocular clinical exam: Involves standardizes techniques such as the evaluation of extra-ocular movement, smooth pursuits, near-point convergence (NPC), horizontal and vertical saccades and the vestibulo-ocular reflex (VOR).
In addition to vestibular and visual dysfunction, other potential causes of persistent dizziness can include cervical spine dysfunction, post-traumatic migraine, and autonomic dysfunction.
- 25 item questionnaire measuring self-perceived disability due to unsteadiness and dizziness. Items are scored from 0-100, with higher scores indicating a greater perceived level of disability. Clinically significant change = 18 or more.
Activities-specific Balance Confidence Scale (ABC) 
- 16-item questionnaire in which patients rate their confidence in their balance during activities of daily living. Items are scored from 0-100, with 100 being complete confidence that they will not lose their balance during a task. Increased risk for falls = score of 67 or less.
Post-Concussion Symptoms Scale (PCSS) 
- 22-item questionnaire requiring patients to rate various symptoms of concussion, vestibular and otherwise, on a scale from 0-6.
Visual Vertigo Scale (VVS)
- Condition-specific, 15-item questionnaire which assesses a patient’s perceived severity of vertigo symptoms over the past month. The scale measures the frequency of vertigo, imbalance, dizziness, and other autonomic and anxiety-related symptoms. Scored out of a total of 60, higher scores indicates increased symptom severity.
When symptoms of concussion such as dizziness, vertigo and imbalance fail to recover spontaneously, vestibular rehabilitation can be used effectively to aid in the normalization of a patient’s vestibular responses. Vestibular rehab involves the use of specific exercises that aim to alleviate symptoms of vestibular dysfunction, as well as improve balance and the overall function of the patient.
- Dynamic Gaze Stability The ability to maintain focus while the head is in motion, controlled primarily by the vestibular ocular reflex (VOR), cervical ocular reflex (COR), smooth pursuit and optokinetic responses. Impairments in the VOR are often seen after an injury to the vestibular system.
- Exercise: “X1” and “X2” viewing - Patient focuses on a target (first stationary, then moving) while the head is rotated. Progressions can include increasing speed and introducing coordination tasks 
- Postural Control Static and dynamic balance - controlled through combined input from the visual, vestibular, and somatosensory systems - can often become impaired following a concussion. Thorough testing needs to be performed to assess all three contributing systems and how they are functioning together for a particular patient. Exercise components:
- Beginning with basic environments and progress to more complex ones
- Eyes open versus eyes closed
- Head turns and tilts
- Stable versus unstable surfaces
- Other Aspects of PCS Treatment
- Pacing techniques
- Graded, sub-symptom exertional exercise 
- Binasal Occlusion (BNO). Partial occluders (scotch tape, nail polish, or electrical tape) can be added to spectacle lenses to suppress abnormal visual motion in the peripheral field. In patients with Visual Motion Sensitivity (VMS), BNO can improve both subjective visual perception and objective performance with sensorimotor tasks.
- It is important to clear patients of Benign Paroxysmal Positional Vertigo (BPPV) prior to beginning vestibular rehab exercises, as it can have its own effect on a patient’s balance and is treated with a specific repositioning protocol.
- Patients should also be screened for cervicogenic dizziness (symptoms caused by cervical spine dysfunction, which should be relieved with manual cervical traction).
- Vestibular rehab is most effective for patients whose headaches are well-controlled, therefore close monitoring of symptoms and treatment coordination with physicians can be important
- A patient does not need to be made dizzy by an exercise in order to improve
- Many mTBI patients require very basic visual targets.
- Consensus statement on concussion in sport: the 4th International Conference on Concussion in Sport held in Zurich, November 2012
- Ontario Neurotrauma Foundation: Guidelines for Concussion/mTBI and Persistent Symptoms: Second Edition
- Guidelines for Concussion/mTBI and Persistent Symptoms: Second Edition. Ontario Neurotrauma Foundation. Available from: http://onf.org/documents/guidelines-for-concussion-mtbi-persistent-symptoms-second-edition Last accessed: 30/08/2016
- Appalachian Regional Healthcare System. What is Post-Concussion Syndrome? . Available from: http://www.youtube.com/watch?v=x59vYzLuQR8 [last accessed 30/08/2016]
- Betteryears.com. Post-Concussion Syndrome Myths and Facts. Available from: http://www.youtube.com/watch?v=srCc6dDWSnY [last accessed 30/08/2016]
- Physical Therapy Nation. Dynamic Visual Acuity Test. Available from: http://www.youtube.com/watch?v=AfghWx3IInE [last accessed 30/08/2016]
- Ellis MJ, Cordingley D, Vis S, Reimer K, Leiter J, Russell K. Vestibulo-ocular dysfunction in pediatric sports-related concussion. J Neurosurg Pediatr. 2015 [cited 2016 May 31]; 16:248-255.
- Jaime Musgrave. Spontaneous nystagmus, gaze holding nystagmus, eye movement range. Available from: http://www.youtube.com/watch?v=USfO3kzzcnY [last accessed 30/08/2016]
- Jaime Musgrave. Vergence 2. Available from: http://www.youtube.com/watch?v=p0c3Upy4NmQ [last accessed 30/08/2016]
- Jaime Musgrave. Saccades. Available from: http://www.youtube.com/watch?v=h6pBbLqKfKI [last accessed 30/08/2016]
- Jaime Musgrave. VOR and VOR Cancellation. Available from: http://www.youtube.com/watch?v=LOrQM0YHyxA [last accessed 30/08/2016]
- Gurley JM, Hujsak BD, Kelly JL. Vestibular rehabilitation following mild traumatic brain injury. NeuroRehabilitation. 2013 [cited 2016 May 31]; 32:519-528.
- Jacobson GP, Newman CW. The development of the Dizziness Handicap Inventory. Arch Otolanryngol Head Neck Surg. 1990;116:424–427.
- Powell LE and Myers AM. (1995). "The Activities-specific Balance Confidence (ABC) Scale." Journals of Gerontology. Series A, Biological Sciences and Medical Sciences 50A(1): M28-34.
- Aubry M, Cantu R, Dvorak J, Graf-Baumann T, Johnston K, Kelly J, et al. Summary and agreement statement of the First International Conference on Concussion in Sport, Vienna 2001. Recommendations for the improvement of safety and health of athletes who may suffer concussive injuries. Br J Sports Med. 2002 Feb;36(1):6-10.
- Dannenbaum E, Chilingaryan G et al. Visual vertigo analogue scale: an assessment questionnaire for visual vertigo. J Vestib Res. 2011. 21(3): 153-159.
- UMHealthSystem. Gaze Stabalization VOR x1 - 2014. Available from: http://www.youtube.com/watch?v=dA_r_dsui6s [last accessed 30/08/2016]
- UMHealthSystem. Gaze Stabilization VOR x 2 - 2014. Available from: http://www.youtube.com/watch?v=aVz_ZD103as [last accessed 30/08/2016]
- St Joseph's London. Concussion/mTBI - Dealing with vision changes: Bi-Nasal Occlusion. Available from: http://www.youtube.com/watch?v=JSFIkCWCwMc [last accessed 30/08/2016]
- Yadav NK, Ciuffreda KJ. Effect of binasal occlusion (BNO) and base-in prisms on the visual-evoked potential (VEP) in mild traumatic brain injury (mTBI). Brain Inj. 2014 [cited 2016 May 31]; 28 (12): 1568-1580.