Introduction

Overview of traumatic brain injury (TBI)

A traumatic brain injury can be caused by either penetrating an object into the skull and entering the brain, such as a bullet or a shattered piece of skull or it can be non-penetrating, induced by an external force moving the brain within the skull, often due to accidental trauma.

Usually, traumatic brain injury is a consequence of a violent blow or jolts to the head, but not all blows or jolts to the head result in a TBI. 

Some forms of TBI can temporarily affect your brain cells, which cause problems with the way you think, understand, move, communicate, and act.  But serious traumatic brain injury can lead to long-term complications like severe and permanent disability or even death¹.

Introduction to intestinal dysfunction 

The term intestinal dysfunction encompasses different problems, including inflammatory bowel disease (IBD), irritable bowel syndrome (IBS), malabsorption syndromes, gastrointestinal motility disorders, functional gastrointestinal disorders, and intestinal ischemia. In these conditions, patients experience common symptoms like abdominal pain, diarrhoea, constipation, bloating, nausea, vomiting, and weight loss.

Relationship between TBI and intestinal dysfunction

Intestinal dysfunction is one of the most common side effects patients experience after a traumatic brain injury (TBI). TBI is believed to increase intestinal permeability, which can cause bacterial translocation, sepsis, and eventually multi-system organ failure.² Although the exact mechanism is not clear, studies assumed that TBI affects the formation of protein ZO-1 and occludin, which are the building blocks of intestinal architecture and integrity, and thus increase intestinal permeability.

Understanding traumatic brain injury (TBI) 

Definition and causes of TBI 

Traumatic brain injury (TBI) results from sudden damage to the brain when any object suddenly hits the head or an object penetrates the skull and enters brain tissues, which affects the normal functioning of the brain. Symptoms of traumatic brain injury (TBI) vary considerably depending upon the condition and severity to which extent trauma is inflicted upon the brain.³

Symptoms and effects of traumatic brain injury 

Traumatic brain injury(TBI) symptoms can appear right away or it develops over time depending upon whether the injury is local or it also includes the surrounding tissues. These symptoms range from mild to severe, contingent upon the extent of damage sustained by the brain. 

Mild symptoms of TBI include: 

• Headache, confusion, dizziness 
• Blurred vision
• Lightheadedness
• Nausea or vomiting
• Ringing in the ears
• Tiredness or sleepiness
• A bad taste perception
• Sleep habits change
• Behaviour or mood changes
• Increased sensitivity to light or sound
• Problems with memory or concentration
• Loss of consciousness lasting a few seconds to minutes

Moderate or severe symptoms of TBI may show these same symptoms but with long duration and high intensity. In addition, the person may experience:

• Loss of vision
• Slurring of speech
• Convulsions or seizures
• Enlargement of the pupil
• Headache that gets worse
• Continued nausea or vomiting
• An inability to wake up from sleep
• Numbness or tingling of arms or legs
• Increased confusion or restlessness
• Loss of consciousness lasting a few minutes to hours⁴

Intestinal dysfunction: An overview 

Definition of intestinal dysfunction 

Intestinal dysfunction refers to any abnormality in the functioning of the intestine that results in digestive problems and associated symptoms like irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), celiac disease, gastrointestinal infections, and functional gastrointestinal disorders (FGIDs).

Symptoms and effects of intestinal dysfunction 

Intestinal dysfunction can be acute or chronic. 

Acute intestinal dysfunction symptoms range from:

• Abdominal pain
• Bloating
• Diarrhoea
• Nausea
• Vomiting and 
• Constipation 
• More severe manifestations like rectal bleeding and weight loss

Chronic intestinal dysfunction significantly influences gastrointestinal health, and patients experience conditions like irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), celiac disease, and other gastrointestinal disorders. It is important to address and manage symptoms at an early stage to avoid any complications.

The connection between TBI and intestinal dysfunction 

Mechanisms underlying the relationship 

Individuals who experience traumatic brain injury commonly face intestinal dysfunction from a mild to severe level and go through conditions like reduced intestinal contractile activity and absorption.⁵ Studies on humans and rodents indicate that TBI disrupts the intestinal barriers which block the flow of certain ions, solutes, proteins, bacteria, and bacterial products and increase intestinal permeability, which play a very important role in pathogenesis and induces a systemic inflammatory response and sepsis with subsequent multiple organ failure.⁶

Evidence from scientific research studies 

Studies demonstrate that traumatic brain injury results to many physiological complications, including chronic intestinal dysfunction and may cause a significant reduction of intestinal contractile activity mostly in the distal intestine and induce an increase in intestinal permeability, which may lead to bacterial translocation, sepsis, and finally multi-system organ failure. However, the exact mechanism of increased intestinal permeability following TBI is unknown.

How TBI impacts gut function and vice versa

Traumatic brain injury (TBI) not only hurts the functioning of the brain but also affects other body parts in many ways. TBI produces a stress reaction that impacts the autonomic nervous system’ (ANS) control of GI function. An acute brain injury also affects the “brain–gut-microbiome axis," a well-balanced network formed by the brain, gastrointestinal tract, and gut microbiome. Which damages the brain and alters the complex composition of the microbiome; the altered microbiome affects TBI severity, neuroplasticity, and metabolic pathways through various bacterial metabolites.⁸

Clinical implications and management strategies 

Research suggests that the bacteria in our gut can change after a traumatic brain injury (TBI). This change, called dysbiosis, seems to make TBI outcomes worse. But, by manipulating these gut bacteria through treatments like probiotics or microbiota transplants, we might improve outcomes for TBI patients. Studies in animals show promising results, like reducing brain damage and improving recovery. Certain bacteria and their byproducts, like short-chain fatty acids, seem to play a role in this process by protecting the brain and improving its energy production. For example, a probiotic called VSL#3 has been shown to improve gut health and help with recovery in spinal cord injury models. In human trials, giving TBI patients probiotics rich in Lactobacilli bacteria early on reduced gastrointestinal problems and lowered infection rates. However, more research is needed to see if probiotics can also improve cognitive and behavioural outcomes in TBI patients and reduce mortality rates.⁹

Conclusion

Traumatic brain injury (TBI) leads to intestinal problems such as increased permeability, bacterial translocation, and systemic inflammation. The exact mechanisms responsible for this relationship are still unknown, but it's clear that TBI can disturb the delicate balance of the brain-gut axis. Clinical indications suggest that manipulating gut bacteria by the use of probiotics may offer promising benefits for improving outcomes in TBI patients. However, further research is required to fully analyze the effect of such interventions on cognitive and behavioural outcomes, as well as mortality rates, in TBI patients. Overall, recognising and addressing the connection between TBI and intestinal dysfunction is important for patient care and outcomes.