Letters to the Editor
I read “Football Concussions Linked to Depression, Cognitive Impairment—Experts Seek Prospective Studies” (Mar. 6, page 1) by Stephanie Cajigal with interest.
Mild concussion in sports is not uncommon, since about 1.5 million people participate in football annually in the US — in recreational, high school, college, and professional settings — with an estimated 4 to 20 percent annual incidence of mild traumatic brain injury (J Neuropsychiatry Clin Neurosci 2005;17:297–303).
Concussion includes any transient loss of neurologic function from biomechanical force and, besides loss of consciousness, may include confusion, disorientation, dizziness, headache, and visual disturbance (J Athl Train 2001;36:228–235). Other sports and activities such as soccer, hockey, and bicycling have risk for concussion. During such head injuries, a neurometabolic cascade is activated with massive release of excitatory neurotransmitters. This has been referred to as “neurotransmitter storm,” followed by neuronal suppression throughout the brain activating membrane pumps and increasing glucose utilization.
Increased glucose demand combined with diminished cerebral blood flow causes a neuronal energy crisis. Increased intracellular calcium interferes with mitochondrial function compounding the energy deficiency in the brain, and possibly triggering cellular pathways leading to cell death
It may take days if not weeks for brain metabolism to return to more normal levels even if the person sustaining the concussion feels relatively well.
Dementia pugilistica due to recurrent traumatic brain injury in boxers has similarities to Alzheimer disease, indicating that recurrent traumatic brain injury may activate similar mechanisms which result in Alzheimer disease (Acta Neuropathol 2001;101:518–524).
It may be important to restrict further participation in the sport after concussions for several days or even weeks, even if the athlete feels well, since the neuronal cascade resulting in brain injury may not have clinical symptoms. Axonal damage has been reported to go on for weeks in brain tissue after trauma.
Repeated injury may activate neuronal processes which occur in Alzheimer disease, resulting in progressive dementia later in life.
Steven Brenner MD
St. Louis VA Medical Center, St. Louis University, St. Louis, MO