By: Brian Hainline, MD
Do females concuss differently than males?
It’s a compelling question among concussion researchers. Despite the intrigue of this question, there is little media attention to this matter. The tendency of the media is to focus on football. The advantage of this column is that I can choose the topics that need to be communicated to a broader audience. Therefore, I am devoting this column to explore concussions in female athletes.
A female’s brain is different than a male’s brain. This is a statement of fact, not judgment. One difference in particular has to do with a female’s susceptibility to migraine between puberty and menopause. During the child-bearing ages, females undergo considerable hormonal fluctuation on a monthly basis in preparation for possible pregnancy. Estradiol in particular reaches peak levels as the uterus becomes prepared for possible embryo implantation, and then drops precipitously if no implantation takes place. Estradiol fluctuation is one of the primary culprits in driving migraine. Before puberty and after menopause, males and females suffer with migraine equally. During child-bearing ages, females are about four times more likely to suffer with migraine. Estradiol interacts specifically with the trigeminal vascular complex, which is an area of the brain that controls migraine pathophysiology.
Why do we care about migraine when discussing concussion in females? Because migraine and concussion share similar pathophysiological expressions. During a migraine aura (often experienced as visual hallucinations), there is an excitatory electrical phenomenon in the brain that is followed by an inhibitory electrical phenomenon. This inhibitory electrical phenomenon is known as ‘spreading depression.’ Spreading depression refers to waves of depressed electrical activity in the brain and has nothing to do with emotions, per se. Think of a pebble that is dropped in a still lake. There are observable waves that emanate from the epicenter of the dropped pebble, and these waves are conceptually similar to the spreading depression waves that occur during a migraine aura. As a result of the progressive inhibitory electrical spread, there is associated neurological dysfunction, ranging from visual loss to difficulty speaking to confusion to vertigo to loss of consciousness.
Scientists have also described spreading depression as an acute manifestation of concussion. Following an impact to the brain sufficient to cause a concussion, there are multiple areas of the brain that may develop spreading depression waves, and this may be an important contributing factor to concussion symptomatology. This also explains why concussion symptoms can worsen for hours following the inciting event. For female athletes during their child bearing years, there is a statistically increased likelihood that a female with migraine susceptibility will become concussed, and such females have a lower threshold to developing secondary spreading depression. In other words, females with migraine susceptibility are more vulnerable to developing worsened symptoms relative to their non-migraine counterpart. At present, the spreading depression hypothesis needs further scientific study; however, it is an intriguing explanation of male-female differences. Spreading depression may help to explain studies that demonstrate the following:
- Female concussed athletes report more concussion symptoms than their male counterparts, including poor concentration, lightheadedness, increased fatigue, headache, and visual hallucinations such as seeing stars.
- Female concussed athletes suffer with greater cognitive decline and slowed reaction time relative to males.
- College female concussed athletes perform more poorly on BESS (Balance Error Scoring System) following concussion relative to males.
In addition to suffering with more concussion symptomatology, females have a higher rate of concussion compared to males when playing the following sports:
- Soccer (2.1 x greater risk)
- Softball versus baseball (up to 3.2 x greater risk)
- Basketball (up to 1.7 x greater risk)
In self-report data that we will explore further in a future column, college female ice hockey players have the highest odds ratio of developing concussion, even when considering football, a male-only event. Thus, female athletes seem uniquely predisposed to suffering with more concussion and worsened concussion symptomatology relative to males. What is startling is that even in lacrosse, female athletes seem to suffer concussion at a similar incidence to males, but female lacrosse is not a contact sport, whereas male lacrosse is a contact sport.
Studies have also demonstrated that females have more injuries due to player-surface contact and player-equipment contact compared to males (males have more injuries from player-player contact compared to females). Females also may have a higher proportion of recurrent concussions compared to males. There may be factors beyond brain physiology that help explain these differences. One aspect of concussion is the biomechanical readiness of protecting the head from sudden acceleration-deceleration and rotational forces. From this framework, females may be at a disadvantage because they have less neck strength than males. This can translate into less ability to counteract mechanical forces that can cause head and neck acceleration-deceleration and rotation. Consider the following statistically significant difference in females compared to males when measuring head-neck strength components and concomitant acceleration forces:
- Females have 25 percent less head-neck segment mass than males.
- Females have 5 percent less head-neck segment length than males.
- Females have 12 percent less neck girth than males.
- Females have 50 percent less isometric neck flexor strength than males.
- Females have 53 percent less isometric neck extensor strength than males.
- Females have up to 44 percent greater head acceleration than males following contact, and have 10 percent greater head accelerations than males during non-contact.
We need to explore female-male concussion differences in more detail. Meanwhile, we all need to spread the word: yes, female athletes also suffer with concussion, and they may be uniquely predisposed to this neurological event.
- Yoshino A et al: Dynamic changes in local cerebral glucose utilization following cerebral concussion in rats: evidence of a hyper- and subsequent hypometabolic state. Brain Research 1991; 1:106-119.
- Hainline B: Migraine and other headache conditions. In Hainline B, Devinsky O (eds): Neurological Complications of Pregnancy, Second Edition, Philadelphia, Lippincott Williams & Wilkins, 2002, pp25-40.
- Lincoln AE et al: Trends in concussion incidence in high school sports: a prospective 11-year study. Am J Sports Med 2011; 39:958-963.
- Marar M et al: Epidemiology of concussions among United States high school athletes in 20 sports. Am J Sports Med 2012; 40:747-755.
- Broshek DK et al: Sex differences in outcome following sports-related concussion. J Neurosurg 2012; 116:856-863.
- Covassin T et al: The role of age and sex in symptoms, neurocognitive performance, and postural stability in athletes after concussion. Am J Sports Med 2012; 40:1303-1312.
- Colvin AC et al: The role of concussion history and gender in recovery from soccer-related concussion. Am J Sports Med 2009; 37:1699-1704.
- Tierney RT et al: Sex differences in head acceleration during heading while wearing soccer headgear. J Athl Train 2008; 43:578-584.