In its fullest form, the characteristic clinical signs of concussive brain injury are the immediate abolition of consciousness, suppression of supportive reflexes (falling to the ground if standing), transient arrest of respiration, a brief period of bradycardia, and fall in blood pressure following a momentary rise at the time of impact. Rarely, if these abnormalities are sufficiently intense, death may occur at the moment of impact, presumably from respiratory arrest. In its mildest form, there is no apparent loss of consciousness or collapse, only a brief period of stunned disorientation, staggering, and amnesia during which the individual appears outwardly normal. The vital signs usually return to normal and stabilize within a few seconds even if the patient remains unconscious.
Brief tonic extension of the limbs, clonic convulsive movements lasting up to approximately 20 s, and other peculiar movements may occur immediately after the loss of consciousness. These “concussive convulsions” are probably of little prognostic significance and have not been shown to confer an increased risk of later seizures. McCrory and Berkovic noted an association between motor and convulsive movements and facial impact, and we have seen this feature several times in teenagers who collided while pursuing a ball.
In the period during which the patient is unconscious and for a few moments afterward, the plantar reflexes are extensor. After a variable period of time, the patient begins to stir and opens his eyes. Corneal, pharyngeal, and cutaneous reflexes, originally depressed, return, and the limbs withdraw from painful stimuli. Gradually, contact is made with the environment and the patient begins to obey simple commands and respond slowly to questions. Memories are not formed during this period; the patient may even carry on a conversation, which he cannot later recall. This aspect of the syndrome closely simulates transient global amnesia, a disorder of obscure cause, discussed in Chap. 20. Finally, there is ostensibly full neurologic recovery corresponding to the time when the patient can form consecutive memories of current experiences.
The time required for the patient to pass through these stages of recovery may be only a few seconds or minutes, several hours, or possibly a limited number of days; but again, between these extremes there seem to be only quantitative differences. To the observer, such patients are unresponsive only from the moment of injury until they open their eyes and begin to speak; however, for the patient, the period of unconsciousness in one limited perspective extends from a point before the injury occurred (retrograde amnesia) until the time when he is able to form consecutive memories at the end of the period of anterograde amnesia. The duration of the amnesic period, particularly of anterograde amnesia, is but one index of the severity of the concussive injury. Although momentary “stunning” without loss of consciousness represents the mildest degree of concussion, as mentioned earlier, it is not known if it shares the same mechanism as overt loss of consciousness. The aftereffects of concussion in causing anxiety, sleep disturbance, mental fogginess and cognitive difficulty, and dizziness are common to both and are discussed further on.