What is considered a functional disorder? Unpacking complex symptoms

October 2, 2025 •

3 min read

According to the National Institute of Neurological Disorders and Stroke, functional neurological disorder is caused by changes in how brain networks work, rather than structural damage. So, what is considered a functional disorder? It's a legitimate medical issue where a person experiences persistent and troubling physical symptoms, but standard medical tests do not find a structural or organic disease.

Quick Summary

A functional disorder is a real medical condition characterized by persistent physical symptoms resulting from a problem with the nervous system's function, not its structure. The signals between the brain and body are disrupted, leading to a range of involuntary symptoms affecting movement, senses, and cognition.

Key Points

Not a fake illness: Functional disorders are real, brain-based conditions where symptoms are not intentionally produced or controlled.
A 'software' issue: Unlike structural diseases, functional disorders involve problems with how the nervous system works, not physical damage to the brain or body.
Variety of symptoms: These disorders can cause a wide range of neurological and physical symptoms, including movement issues, seizures, pain, and fatigue.
Diagnosis by inclusion: A diagnosis is made based on specific clinical signs and patterns observed by a neurologist, not simply because other tests come back normal.
Multifactorial causes: The cause is often a combination of biological, psychological, and social factors, and not necessarily triggered by a specific trauma.
Multidisciplinary treatment: Successful treatment involves a team approach, often including physical therapy and psychotherapy like CBT.

Understanding the 'Software Glitch'

A functional disorder is a medical condition characterized by symptoms resulting from issues with the nervous system's function, rather than structural damage or disease. It's often described as a "software glitch" in the nervous system, where the brain and body's communication is disrupted. While diagnostic tests like MRI or CT scans typically appear normal, the nervous system is not functioning correctly, leading to real and involuntary symptoms that can cause significant disability.

Common examples of functional disorders

Functional disorders encompass a variety of conditions, including:

Functional Neurological Disorder (FND): Affecting the nervous system, FND can cause symptoms like weakness, seizures, tremors, and sensory issues. It includes conditions previously termed 'conversion disorder'.
Irritable Bowel Syndrome (IBS): A functional gastrointestinal disorder involving abdominal pain, bloating, and altered bowel habits without visible damage to the digestive tract.
Fibromyalgia: A functional somatic syndrome characterized by widespread chronic pain, fatigue, and cognitive difficulties.
Functional Movement Disorder (FMD): A type of FND causing involuntary movements or abnormal postures.
Chronic Fatigue Syndrome (CFS): A long-term illness causing persistent fatigue and other symptoms, also known as myalgic encephalomyelitis (ME).

The diagnosis journey: Clinical signs vs. normal tests

Diagnosing functional disorders can be challenging because standard tests often yield normal results. However, diagnosis, particularly for FND, relies on a neurologist identifying specific positive clinical signs that are inconsistent with known neurological diseases. Examples of such signs include Hoover's sign (hip weakness when lying down but not with other movements), co-activation sign (weakness resolving with opposing limb force), and symptom inconsistency, such as a tremor that changes with distraction.

Comparison: Functional vs. Structural Disorders


Feature	Functional Disorders	Structural/Organic Diseases
Underlying Problem	Dysfunction in how the nervous system operates; a "software" issue.	Physical damage or disease to the body's structures, such as organs or tissues.
Diagnosis	Primarily clinical, based on positive signs and patterns.	Often confirmed by diagnostic imaging (MRI, CT) or laboratory tests.
Test Results	Imaging (MRI/CT) and other structural tests are typically normal.	Tests often show clear evidence of structural damage or disease.
Symptoms	Real, involuntary symptoms (e.g., weakness, non-epileptic seizures, chronic pain).	Real, involuntary symptoms caused by physical disease (e.g., stroke, MS).
Nature of Symptoms	Often come and go, may be inconsistent or triggered by stress.	Typically more consistent with a pattern of physiological disease.
Overlap	Can coexist with structural disorders and other mental health conditions.	Can also have functional components, but the primary cause is structural.

Causes, Triggers, and Risk Factors

The causes of functional disorders are complex and vary among individuals. They are considered multifactorial, involving a combination of biological, psychological, and social elements. Potential triggers and risk factors include stress, trauma (emotional or physical), pre-existing health conditions (neurological or mental health), possible genetic predispositions, and even negative experiences with healthcare. Functional disorders are also more commonly observed in women, though diagnostic bias may contribute to this.

Treatment and Outlook

With early diagnosis and acceptance, the outlook for individuals with functional disorders is often positive. Treatment is typically multidisciplinary and tailored to the individual. This can involve physical or occupational therapy to retrain movements, cognitive behavioral therapy (CBT) to help manage symptoms and related distress, and sometimes medication for co-occurring conditions like anxiety or depression. Distraction techniques can also be helpful in managing symptoms.

Conclusion

The understanding of what is considered a functional disorder has evolved, recognizing it as a legitimate, brain-based condition stemming from nervous system dysfunction rather than structural damage. While challenging to diagnose due to normal test results, modern approaches focus on identifying specific clinical signs. With early intervention and a comprehensive, multidisciplinary treatment plan that includes therapies and education, many individuals can effectively manage their symptoms and improve their quality of life.

Frequently Asked Questions

No, the symptoms of a functional disorder are not imagined. They are real and can cause significant distress and disability, but they stem from a problem with the nervous system's function, not its structure.

Diagnosis is based on a neurologist's clinical assessment, looking for specific, positive clinical signs that are inconsistent with known neurological diseases. It is not made by simply ruling out other conditions.

Yes, stress or psychological trauma can sometimes trigger functional disorders in some individuals, but a clear trigger is not always present. Other factors like physical illness, injury, or biological predispositions can also play a role.

Functional Neurological Disorder (FND) is the current and preferred term. It is a broader and more neutral term that encompasses the same conditions, moving away from the stigmatizing implications of 'conversion disorder'.

Treatments are often multidisciplinary and may include physical therapy, occupational therapy, cognitive behavioral therapy (CBT), and sometimes medication to address co-occurring conditions like anxiety or depression.

Yes, it is possible for a functional disorder to coexist with another condition. For example, some individuals may have both epilepsy and functional seizures, and it is important to treat both conditions appropriately.

Yes, recovery is possible, especially with an early diagnosis and a comprehensive, tailored treatment plan. The outlook is generally good for those who can understand and accept the diagnosis and are committed to their treatment.