top of page

Functional vs structural disease and the stigma associated with the functional label

Updated: Nov 30, 2023

Form follows function—that has been misunderstood. Form and function should be one, joined in a spiritual union. Frank Lloyd Wright, Architect

“Nothing sinister,” wrote my gastroenterologist in the clinical notes. The unexplained weight loss that left my bones sticking out felt sinister. The bouts of weakness and disorientation threatened trouble. The abdominal pain, like tiny soldiers stabbing my stomach from the inside out, was surely a product of evil. “Nothing sinister” mocked me. As though delivering good news, the doctor explained my illness is functional, not structural. He told me my ailments are part of a ‘sensory disorder’ and diagnosed me with ‘functional bowel disease’.

Functional disease refers to a medical condition with no detectable physical cause. These disorders take several names: functional, sensory, somatic and conversion disorders. Functional disorders are believed to be caused by psychological trauma, and they disproportionately affect women and those assigned female at birth.

I got acquainted with functional disorder when I was twenty. My limbs started shaking and contorting against my will for brief, but frequent episodes. I felt strange being a passenger in my own body. My doctor found no neurological cause—no epileptic activity and no tumour, only low blood sugar. After waiting four months to see a neurologist specialised in movement disorders, after anticipating relief, the specialist diagnosed a conversion disorder called ‘functional movement disorder’ and recommended mental health therapy. I was devastated. Therapy made no impact on my involuntary movements. Months later, I presented to a cardiologist with chest pain. Again, I was diagnosed with ‘functional cardiac pain’ and given no treatment.

The name ‘conversion disorder’ is a modern term for hysteria, yet it is widely accepted, while hysteria is recognised as an outdated and unscientific diagnosis. The hysteria label dismisses ailments affecting women, who face higher rates of chronic illness. Physicians in the post-Freud era of the 20th century blamed hysteria on repressed trauma, though the original cause was thought to be a ‘wandering womb’. Historically, hysteria treatments have ranged from marriage, pregnancy, zinc oxide, heterosexual sex, isolation, electrotherapy, physical therapy, psychotherapy, anxiety medication and antidepressants. In modern medicine, functional disorders are thought to reflect psychological trauma manifesting as physical sensation, with no underlying pathology. Chronic fatigue syndromes (CFS), irritable bowel syndrome (IBS) and fibromyalgia are often considered functional/somatic disorders.

A group of people in a room
A Clinical Lesson at the Salpêtrière by Pierre Aristide André Brouillet, 1887

Is functional disease supported by evidence?

Recent research shows many cases of Functional Neurological Disorder (FND) occur in the absence of trauma or anxiety. FND responds better to physical therapy than psychotherapy. Chronic fatigue syndrome (also called myalgic encephalomyelitis) is a biological disorder characterised by immune cell dysfunction. The highest risk factor for irritable bowel syndrome is infection, not psychological stress. Fibromyalgia is linked to increased inflammation and activation of brain cells that process pain. The notion that ‘functional disease’ is independent of structural abnormalities is contradicted by an abundance of evidence.

Treating trauma is not treating disease

While not all functional diseases arise in response to trauma, some cases do. Research on adverse childhood experiences (ACEs) shows that early life trauma can lead to inflammation and changes in gene expression. Once dysfunction occurs, is trauma a useful framework for treating disease? Reducing stress is always a good idea, but managing psychological issues is no replacement for treating physical disease. Trauma is highly associated with high blood pressure, multiple sclerosis and cardiovascular disease. Should a doctor deny someone with high blood pressure their medication because stress was related to disease onset? Should a doctor send a patient with multiple sclerosis to a psychotherapist instead of a neurologist? We can abandon the belief that ‘functional disease’ has no structural cause, while accepting a model of disease that acknowledges psychosocial influences on disease.

Structure and function outside of medicine

In the human body, form and function are deeply related. The double-helix structure of DNA allows it to replicate swiftly. Bones provide humans with structural support and produce blood cells. The structure of a pelican’s beak allows it to store fish for long flights. Outside of biological systems, structure and form are deeply related. In businesses, flat organisation structures lead to innovation and swift action, while hierarchical structures support accountability and quality control. In architecture, form and function are intertwined. Why is medicine an exception?


Many clinicians, faced with unexplained illness, are trained to suspect somatic disorders before admitting ignorance. One research paper associates the misdiagnosis of organic disease as functional disease with a physician’s “unconscious wish to discontinue clinical responsibility in a situation that threatened his self-esteem”. 12% of patients with functional neurological disorder are determined to have an underlying medical condition upon clinical re-evaluation. Rare disease patients, with complex multi-system symptoms, often end up misdiagnosed with functional disorders.

My ‘functional disease’

My functional bowel disease, functional neurological disorder and functional cardiac pain turned out to share a common pathology: a rare mitochondrial disorder. My condition is characterised by heart weakness, muscle dysfunction (including involuntary movements), gut disturbances and low blood sugar. Mitochondrial dysfunction is a structural issue on the cellular level with widespread functional consequences. Mitochondrial dysfunction leads to disruption in cellular communication and energy production.

Work ahead of us

Despite the widespread evidence of biological causes behind ‘functional disorders,’ shifting consensus will be challenging. A 2023 review of FND by Italian physicians, published in the popular journal Frontiers, argues that many patients with FND also have ‘factitious disorder’. Factitious disorder is defined by (1) intentionally faking symptoms and (2) no external incentive for faking symptoms. According to the DSM, a manual for diagnosing psychiatric illness, ‘factitious disorder’ is caused by the “compulsion to act out a sadomasochistic relationship with physicians regarded as parental figures.” In plain language, unexplained illness is caused by patients acting out their subconscious desire for power struggles with their physician. The acceptance of this pseudoscientific, Freudian belief and the publication of such belief in an established, peer-reviewed journal, should alarm and appal any reasonable person. There is nothing pleasurable about the suffering undiagnosed patients endure. 11–30% of patients in neurology clinics present with FND or medically unexplained symptoms. Do we all feign non-epileptic seizures, diarrhoea, chronic pain and more because deep down we long for a relationship with our physicians?

Medicine has a legacy dating back to 1900 BC of blaming women’s health mysteries on hysteria. Old habits die hard. Thankfully, many compassionate and innovative physicians are adopting better ways to address functional disease, i.e. medically unexplained symptoms. When the underlying cause cannot be determined, rare disease should be considered. To treat unexplained symptoms, physicians should adopt a functional medicine approach, characterised by listening to patients’ narratives, prioritising lifestyle factors, adopting a systems biology framework and creating a therapeutic partnership between the patient and doctor. Other critical steps that patient advocates, policymakers and scientists can take include educating physicians on rare disease, improving access to genetic testing and disseminating updated evidence on the management of functional disorders.

Physicians brand patients with ‘functional’ disease when no structural problem is detected, and when the structural problem occurs at a level—or a pervasiveness—that a specialist is not accustomed to, like disruption in mitochondria or cytokine signalling. The concept of functional disorder rests on the assumption that knowledge is complete, for a doctor must rule out all possible structural issues. It rests on the belief that function operates independently of structure. My misdiagnosis led to over a dozen doctor visits, distress, out-of-state appointments and disease progression. My story is all too common among rare patients. We can and must do better. I am optimistic that the next generation of physicians will challenge outdated beliefs and approach unexplained medical symptoms with patience, humility and compassion.



Instagram: kaate98

LinkedIn: Kathryn Cowie


bottom of page