What you need to know:

The Centers for Disease Control and Prevention (CDC) estimate between 1.6 and 3.8 million recreational and sports-related concussions occur annually in the U.S., and 10% of persons participating in contact sports experience concussions each year. Patients that have suffered three or more concussions are at risk for long-term complications, such as chronic traumatic encephalopathy.  This condition is characterized by large deposits of tau proteins in the brain and manifests as early onset of memory loss and depression.

A concussion is considered a mild form of traumatic brain injury. In the past, the cardinal symptom of concussion was brief loss of consciousness, but it is now recognized that this is not required for diagnosis. Individuals that experience concussion do not necessarily lose consciousness, but may experience acute confusion, or describe a state of feeling “dazed” or “faint”. Some patients may demonstrate transient autonomic signs such as bradycardia and pallor.  Other symptoms typically persist 1-2 days and may include blurred vision, fatigue, dizziness, headache, nausea, vomiting, and irritability. About 15% of patients do not experience resolution of these symptoms in the usual 1-2 day timeframe, but experience persistent symptoms for weeks to months.  This phenomenon in known as post-concussion syndrome. Concussions are graded according to severity.

A concussion usually occurs following a blunt force injury to the head. This injury is mild, and typically does not cause fracture or bleeding. No CT or MRI abnormalities are present. The loss of consciousness that often occurs following a concussion is not fully understood. 

ACM Resources to help you learn more:

"Concussion and Other Traumatic Brain Injuries" in Harrison's Principles of Internal Medicine, 19e

"Head Trauma" in Tintinalli’s Emergency Medicine: A Comprehensive Study Guide, 8e

"Head Injuries" CURRENT Diagnosis & Treatment: Emergency Medicine, 8e 

"Confusional States" in Clinical Neurology, 10e