Concussion

What it is

A traumatic brain injury (TBI) is damage to the brain caused by an outside force, such as a bump, blow or jolt to the head or body¹⁰. Concussion is a form of mild TBI, and expert criteria state that the terms concussion and mild TBI may be used interchangeably when brain imaging is normal or not needed^2,10.

Concussion can happen in falls, road traffic collisions, sport and assaults, and it may involve either a brief loss of consciousness or simply a sudden change in awareness¹⁰. In high-income countries, falls, particularly among older people, cause most brain injuries³.

Most people recover fully within a few weeks, but recovery varies^8,10. In a large United States study of people treated at major trauma centres, 53% of those with mild TBI still reported some injury-related limitation in daily life a year later⁷.

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Rapid movement of the brain can stretch and injure axons, the long fibres that make up the white matter¹⁰. Diffusion imaging can detect such injury when routine scans are normal³.

Signs and symptoms

Headache, dizziness, confusion and tiredness tend to start soon after the injury, while emotional symptoms such as frustration and irritability often develop during recovery¹⁰. Young children may not be able to describe how they feel, so changes in behaviour, feeding or sleep can be important signs¹⁰.

• Headache, nausea and feeling dizzy or off-balance¹⁰
• A brief loss of consciousness, or feeling dazed, confused or disoriented¹⁰
• Problems with memory, concentration or making decisions¹⁰
• Blurred vision, sensitivity to light or sound, or ringing in the ears¹⁰
• Tiredness and changes in sleep¹⁰
• Irritability, mood changes, anxiety or low mood¹⁰

Causes and risk factors

Concussion is caused by forces that move the brain rapidly within the skull, either from a direct blow to the head or from a sudden jolt to the body¹⁰. Not every blow to the head causes a brain injury¹⁰.

• Falls, especially in older people, who often have other health conditions³
• Road traffic incidents, a leading cause in low- and middle-income countries³
• Contact and collision sports^1,10
• Blast exposure in military settings¹⁰
• Being struck by an object or violently shaken¹⁰
• Frailty and alcohol misuse, which are recognised risk factors and targets for prevention³
• A previous concussion, since recovery from a second or third concussion is generally slower¹⁰

Genetics

Concussion is an injury, not an inherited condition, so genetics plays only a limited role. Genetic differences may influence how people recover, and genetics is one of several factors being studied to improve predictions of outcome after brain injury³.

What happens in the brain

Rapid movement of the brain inside the skull can stretch and injure nerve fibres (axons), the long projections that carry signals between neurons¹⁰. Immediately afterwards there is an abnormal flow of charged particles (ions) across nerve-cell membranes and a release of glutamate, a chemical messenger that excites neurons⁴.

Restoring the normal balance of ions demands a great deal of energy, producing a temporary period of metabolic crisis in brain cells⁴. These changes have been linked to typical symptoms such as headache and cognitive problems, and to a period of increased vulnerability to a further injury⁴.

Standard brain scans are usually normal after concussion, but MRI can show structural damage in up to 30% of people with mild TBI, and advanced techniques such as diffusion tensor imaging can detect injury to white-matter pathways that routine images miss³.

How it is diagnosed

Concussion is diagnosed clinically, from how the injury happened, the symptoms and an examination, because no single test can confirm it^2,10. Criteria from the American Congress of Rehabilitation Medicine, developed through expert consensus, aim to standardise diagnosis across sport, civilian and military settings².

The first priority is to identify the small number of people with bleeding or other serious injury inside the skull. In the United Kingdom, NICE guidance covers the assessment and early management of head injury, including when direct referral to specialist care is needed⁹.

• Recognition at the scene in sport, using tools such as the Concussion Recognition Tool¹
• Structured assessment with tools such as the Sport Concussion Assessment Tool (SCAT6) and, later, office-based follow-up tools¹
• The Glasgow Coma Scale, a score of eyes, speech and movement responses; mild TBI is usually defined as a score of 13-15³
• CT scanning when warning signs suggest bleeding or other injury inside the skull³
• Blood tests for the brain proteins GFAP and UCH-L1, which can help rule out the need for a CT scan in some adults^3,5
• Neuropsychological tests of memory, attention and reaction time, which help track recovery¹⁰

How scientists study it

Current treatments

Research frontiers

Living with the condition and seeking help

Emergency help should be sought straight away after a head injury if the person has been knocked out and has not woken, cannot stay awake, has a seizure, has problems with vision or hearing, has clear fluid from the ears or nose, has new weakness or numbness, or has problems with speaking, walking or balance⁸. Urgent medical advice is recommended for vomiting, dizziness, use of blood-thinning medicines, or alcohol or drug use at the time of injury⁸. In India, the national emergency number is 112 and the ambulance number is 108^11,12.

For a minor head injury, an adult should stay with the injured person for at least the first 24 hours⁸. People should not drive until fully recovered and should return to work or school only when they feel better⁸.

Children and teenagers with a sport-related concussion should stop playing immediately and return only after approval from a concussion specialist¹⁰. A doctor should be seen if symptoms last longer than 2 weeks or if there is uncertainty about returning to driving, work, school or sport⁸.