Introduction

Definition of klüver-bucy syndrome (KBS)

Klüver-Bucy syndrome (KBS) is a rare brain disorder resulting from lesions in the temporal lobes, located on both sides of the brain.¹ Figure 1 shows where the temporal lobes are located. The temporal lobes contain two important structures: the hippocampus and amygdala, shown in Figure 2.¹ 

The hippocampus is essential for creating new memories and storing information for future reference, playing an important role in decision-making.² The amygdala is like the brain’s ‘emotional hub’ – it helps to process emotions.³ The amygdala is also involved in social cognition, the ability to read facial expressions, and understanding social interactions.³

Figure 1: Figure 1 shows the four lobes of the brain. The temporal lobe is shown in green. (Adapted from Biorender)

Figure 2: Figure 2 shows where the amygdala and hippocampus are located, in dark blue and light blue, respectively. (Adapted from Biorender)

In KBS, the temporal lobes are damaged, which causes cognitive and behavioural symptoms.¹ 

These include:

• Hypersexuality 
• Hyperorality (examining objects through the mouth) 
• Hyperphagia 
• Bulimia 
• Visual agnosia (having the ability to see but not being able to recognise visual stimuli)
• Placidity (loss of aggressiveness and lack of fear/anger responses)¹ 

Diagnosis occurs if a person presents with three or more of the symptoms of KBS.⁵ The syndrome can be considered either partial (incomplete) or full (complete).¹¹ A patient who has the entire spectrum of symptoms has full KBS.¹¹ If a patient only shows some symptoms, they are considered to have partial or incomplete KBS¹¹. Complete KBS is rarely seen.¹¹

Importance of understanding the underlying causes

KBS can affect anyone, including both adults and children.¹ The causes of KBS vary from person to person, with common causes including: 

• Brain damage 
• Infections 
• Neurodegenerative disorders and tumours⁴ 

It is important to understand the underlying causes of KBS,  as they directly relate to the treatments introduced by clinicians. Therefore, it is essential that patients with KBS receive individualised treatment. Assessing the cause helps to guide clinicians, patients and their families about the prognosis of the condition, and how to manage symptoms. 

Brain damage

Traumatic brain injury (TBI)

Traumatic brain injury (TBI) is a common cause of KBS.¹ Following a TBI, KBS manifestations may differ from one patient to another. In some patients, KBS can last for a longer period of time.⁵ For others, KBS may last for a shorter period.⁵ In a study conducted on KBS following a TBI, it was found that KBS symptoms appeared early on after a TBI. In 12 cases, symptoms occurred less than 7 days after a TBI, and in 5 cases, symptoms appeared between 7 to 31 days post-TBI.⁵ In two cases, symptoms appeared a year after a TBI took place.⁵ 

The cases mentioned refer to more severe TBIs. However, a case study shows that more frequent, minor TBIs can eventually cause KBS symptoms to manifest. In the case of a 39-year-old man with a history of untreated closed head injuries, he showed some symptoms of KBS such as hyperphagia, hypersexuality and amnesia.⁶ An MRI (magnetic resonance imaging) of the brain showed abnormalities in the left temporal lobe. Even if a TBI is minor, and in this case was untreated previously, eventually it could lead to the development of KBS.⁶

Although there is a link between TBI  and KBS symptoms, it is unclear why some cases exhibit symptoms earlier than others.

Surgical procedures

Surgical procedures can, in some cases, induce KBS symptoms. An example of this is temporal lobectomy, which is used for conditions including epilepsy.⁷ However, the removal of a part of the temporal lobe can cause KBS symptoms to occur postoperatively. 

In the case of a 70-year-old woman diagnosed with a malignant brain tumour in the left anterior temporal lobe, she was treated with a left anterior temporal lobectomy. This involved the removal of some of the left temporal lobe, including removing some of the amygdala, but leaving the hippocampus intact.⁸ Despite this, the patient still developed all of the key symptoms of full KBS, even with just one temporal lobe affected.⁸

Infections leading to KBS 

Herpes simplex encephalitis

Herpes simplex encephalitis (HSE) is a serious condition caused by the herpes simplex virus type 1 (HSV-1) or herpes simplex virus type 2 (HSV-2).⁹ HSV-1 is more common, affecting both adults and children.⁹ HSE is considered a type of viral encephalitis, which is brain inflammation caused by an infection, and can be life-threatening.¹⁰ HSE affects the temporal lobes.¹²

In a case study of a 21-year-old man with no relevant medical history, he showed symptoms of HSV-1 encephalitis.¹² He was treated accordingly and began to display symptoms of hypersexuality, hyperphagia and was diagnosed with KBS.¹² 

Three months later, he continued to show symptoms despite carbamazepine (a medication that helps with behavioural changes like hypersexuality) being used. It is thought that the HSE was treated later, which resulted in damage to the temporal lobes and therefore why the patient’s symptoms continued to persist.¹²

Chronic infections and brain inflammation

Other infections have also been associated with the development of KBS. Tuberculosis meningitis (TBM) is an infection in the central nervous system (CNS).¹⁴ The CNS is made up of the brain and the spinal cord.¹⁴ TBM is caused by the bacteria Mycobacterium tuberculosis (MTB) and causes inflammation of the meninges, the membranes surrounding the CNS.¹⁵ TBM can be life-threatening if not treated promptly.¹⁵ As a result of TBM, a patient can start to show symptoms of KBS.¹³ 

In a case study in India, a patient was sent to a hospital due to displaying abnormal behavioural symptoms for 2 months.¹³ Thirteen months previously, the patient presented with a fever, but multiple treatments did not result in any relief. He was prescribed anti-tubercular drugs for 15 days, and once his symptoms were reduced, the medication was stopped.¹³ Unfortunately, after a month of no medication, he was admitted to the ICU (intensive care unit) and diagnosed with TBM after an MRI report. 

After being treated for TBM, he was discharged and had now been experiencing abnormal behavioural symptoms.¹³ An MRI was conducted and showed that both the temporal lobes had been affected.¹³ He was diagnosed with partial KBS and was treated with an antipsychotic drug, which significantly minimised his symptoms.¹³

Neurodegenerative and metabolic disorders

Neurodegenerative disorders 

Neurodegenerative diseases can also be associated with symptoms of KBS.

Alzheimer’s disease (AD) is a neurodegenerative condition that leads to progressive difficulties in memory, learning and behaviour.¹⁶ Alzheimer’s disease is the most common cause of dementia.¹⁶ Pick’s disease, also known as frontotemporal dementia (FTD), is a more common cause of dementia in patients under the age of 60.¹⁷ Alzheimer’s disease is associated with memory loss as a more common early symptom, whereas Pick’s disease is often associated with language and behavioural symptoms.¹⁷

In a case study, a 70-year-old man presented with memory difficulties and behavioural changes.¹⁸ He continued to display symptoms such as hypersexuality and hyperphagia until his death at the age of 77.¹⁸ 

He was initially diagnosed with FTD due to the abnormal behavioural symptoms he presented with.¹⁸ However, significant abnormalities in the amygdala were found, which is consistent with the presentation of Alzheimer’s disease.¹⁸ This shows that the damage in the amygdala, due to AD, may have caused the symptoms associated with KBS, especially hyperphagia and hypersexuality.

Glycogen storage disease type Ib (GSD Ib)

Metabolic disorders have been found to be linked to KBS. Glycogen storage disease type Ib (GSD Ib) is an autosomal recessive disorder caused by a deficiency of the glucose-6-phosphate transporter.²⁰ This deficiency means glycogen in the body cannot be made into glucose, which causes an excess of glycogen in the liver and kidneys.²⁰ Symptoms of GSD Ib include hypoglycaemia and an enlarged liver.²⁰

In a case study of a 28-year-old man with GSD Ib, he developed a respiratory infection and struggled to eat.¹⁹ As a result, he developed severe hypoglycaemia and fell into a coma. After the coma, he developed symptoms of KBS.¹⁹ This is thought to be due to the prolonged hypoglycaemia, which caused brain damage, and therefore resulted in the development of KBS.¹⁹

Summary 

KBS is a rare disorder with a number of symptoms, ranging from hypersexuality to hyperphagia and can affect both adults and children alike. KBS occurs when the temporal lobes in the brain are affected. The temporal lobes contain the brain’s memory centre, the hippocampus and the brain’s emotion hub, the amygdala. 

KBS is affected by brain damage through a TBI, or surgery for epilepsy or tumour removal. KBS can also be caused by neurodegenerative diseases such as AD, which affects the amygdala in the temporal lobe and causes symptoms. Other causes of KBS include metabolic disorders and substance misuse. 

The underlying cause of KBS in each individual should be identified promptly, as this is essential for timely diagnosis, effective treatment, and ultimately reducing symptoms. Treatment of KBS for individuals should be tailored to ensure a better prognosis and patients being able to return to their normal state of activity.

Frequently asked questions 

What is klüver-bucy syndrome?

Klüver-Bucy syndrome (KBS) is a rare syndrome caused by damage to the temporal lobes in the brain. 

What is the most common cause of klüver-bucy syndrome?

In adults, the most common cause of KBS is a traumatic brain injury or a stroke.¹ In children, the most common cause of KBS is encephalitis.¹

What are the symptoms of klüver-bucy syndrome?

It is characterised by symptoms such as hyperphagia (excessive eating), hypersexuality, amnesia, and placidity (no fear/anger response).