Second-impact syndrome (SIS) refers to the catastrophic events which may occur when a second concussion occurs while the athlete is still symptomatic and healing from a previous concussion(2). The second injury may occur from days to weeks following the first. Loss of consciousness is not required. The second impact is more likely to cause brain swelling and other widespread damage, and can be fatal.
However, the true incidence and impact of SIS remains a thorny issue. A total of 17 cases have been reported in the literature, and only five cases had confirmed diagnoses of SIS(6). Thus, the claim that SIS is a risk factor for diffuse cerebral swelling has not been supported in the literature.
Most clinicians understand that following a significant head impact, athletes with any symptoms of concussion should not return to the sports activity until examined by a physician, and until they are symptom-free. However, knowing that an athlete is truly asymptomatic is very difficult to discern. In the absence of a positive finding on head CT, and without baseline neurocognitive data, a truly informed decision is difficult to make(4).
Clinicians are now recommended to perform simple, baseline cognitive testing on any individual athlete or sports team for which they are responsible. Baseline measures are important to collect PRE-season before any mild injuries may occur(8). The American Academy of Neurology has published a brief Sideline Assessment of Concussion which is short, repeatable, and easily administered (see Table 2). This measure, or other simple neuropsychological tests, can be used to assess athletes at baseline, with repeated administration following an injury. Comparison of post-injury data to baseline neurocognitive function can inform physicians as to when patients truly have no remaining neurological impairment.
Other than cognitive changes, which may be subtle and which may only be able to be evoked with standardized testing, additional warning signs of concussion include:
• Vacant stare (befuddled facial expression)
• Delayed verbal and motor responses (slow to answer questions and follow instructions)
• Inability to focus attention (easily distracted and unable to follow through with normal activities)
• Disorientation (walking in the wrong direction; unaware of time, date and place)
• Slurred or incoherent speech (making disjointed or incomprehensible sentences)
• Gross observable incoordination (stumbling, inability to walk tandem/straight line)
• Emotionality out of proportion to circumstances (distraught, crying for no apparent reason)
• Memory deficits (exhibited by the athlete repeatedly asking the same question that has already been answered, or inability to memorize and recall three of three words or three of three objects in five minutes)
• Any period of loss of consciousness (paralytic coma, unresponsiveness to arousal)