Functional Neurological Symptom Disorder, historically known as Conversion Disorder, is a complex condition where individuals experience neurological symptoms without a clear underlying medical explanation. These symptoms, though not attributable to a neurological disease, are genuinely experienced and can significantly impact daily functioning. Understanding this disorder is an initial step toward comprehending its commonality and the nuances involved in its identification.
What is Conversion Disorder?
Conversion Disorder, now called Functional Neurological Symptom Disorder (FND) in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), involves altered voluntary motor or sensory function. Symptoms include weakness or paralysis of a limb, impaired coordination or balance, speech difficulties such as aphonia or slurred speech, and sensory disturbances like numbness, blindness, or deafness. Psychogenic non-epileptic seizures, resembling epileptic fits but lacking typical brain activity, are also common. These symptoms are not intentionally produced and are incompatible with recognized neurological or medical conditions. The disorder can significantly interfere with a person’s social, occupational, or other important areas of functioning.
Prevalence and Incidence Rates
Determining the commonness of Functional Neurological Symptom Disorder is complex, with prevalence and incidence rates varying across studies due to methodological differences. General population prevalence estimates for FND range widely, from 80–140 per 100,000 people to 50–1600 per 100,000. Some older estimates for Conversion Disorder placed lifetime prevalence between 11 and 300 cases per 100,000 persons.
Incidence rates, representing new cases per year, are estimated at 10–22 per 100,000 adults, and for pediatric populations, this figure is between 1 and 18 per 100,000. The disorder is encountered more frequently in clinical settings than in the general population. FND is a common reason for neurological consultations, accounting for 15% of new outpatient visits in some neurology clinics, making it the second most frequent reason after headaches. In general hospital settings, 5–14% of patients may have FND, while psychiatric outpatient clinics report prevalence rates between 5% and 25%.
Demographic and Clinical Influences
Demographic factors play a role in the observed patterns of Functional Neurological Symptom Disorder. The condition is often reported as more common in women, with female-to-male ratios ranging from 2:1 to 10:1, though this can vary by symptom type and reporting biases. While FND can affect individuals across the lifespan, it is frequently diagnosed in young adults, typically between 10 and 35 years of age, and is less common in very young children or the elderly.
Socioeconomic status and geographic location also show some associations, with higher prevalence rates noted in rural populations and those with lower socioeconomic status or less education. Functional Neurological Symptom Disorder often co-occurs with other mental health conditions. High rates of anxiety disorders, depression, and post-traumatic stress disorder (PTSD) are frequently observed in individuals with FND, with comorbidities reported in 40% to 100% of patients.
Diagnostic Challenges and Accurate Reporting
Diagnosing Functional Neurological Symptom Disorder presents inherent challenges that can influence the accuracy of prevalence data. The diagnosis relies on positive signs and symptoms that are inconsistent with known neurological diseases, rather than solely on the absence of a medical explanation. For example, specific physical examination findings, like Hoover’s sign for functional weakness or entrainment for functional tremor, help confirm the diagnosis.
The DSM-5 criteria for FND emphasize that symptoms must involve altered voluntary motor or sensory function, show incompatibility with recognized medical conditions, and not be better explained by another disorder. Changes in diagnostic criteria over time, such as the DSM-5 removing the requirement for an explicit psychological stressor, have refined the diagnostic process and can affect reported prevalence figures. Misdiagnosis or underdiagnosis can occur, but recent studies suggest the rate of misdiagnosis for FND by neurologists is relatively low (5% to 10%), comparable to other neurological conditions.