Functional neurological disorder (FND) is classified in the DSM-5-TR as “functional neurological symptom disorder (conversion disorder)” and in the chapter on mental disorders of the ICD-11 as “dissociative neurological symptom disorder”.

Neurologists, who most commonly make the initial diagnosis, are usually barely aware of such classification systems, and use a variety of terms – such as “functional”, “psychogenic” or “non-organic” – to describe symptoms of paralysis, tremor, seizures or blindness that were once encompassed under the label of “hysteria”. This diversity of terms reflects a disorder that has been passed back and forward between neurology and psychiatry for 150 years. Over time, the FND pendulum has swung between a brain disorder in the late 19th century to a purely psychological condition in the 20th century. Today, FND researchers are suggesting that the pendulum rest in the middle. Defying dualism in FND may cause dissonance in clinicians, in those seeking tidy explanatory theories, and in classification systems. But it is an essential platform towards understanding FND and improving care for the millions of people around the world who have it.

For those who grew up with “conversion disorder” in the DSM-IV, the idea was simple, hydraulic and comfortingly Freudian. Someone has a stressful event, which is repressed and converted to motor or sensory symptoms, that may or may not be symbolic, perhaps reducing the stress, sometimes to the point of belle indifférence. Conversion disorder was often considered a rare condition, which could only be diagnosed by exclusion, and would often respond quickly to psychological therapy. Historian E. Shorter declared that “hysteria” had largely disappeared in favour of other somatic symptoms such as fatigue¹.

In the last 20 years, this narrow view of the condition has been systematically dismantled by the evidence. FND is a common condition, one of the commonest seen by neurologists in both outpatient and inpatient settings, making up 5-15% of patients². It accounts for 50% of people rushed into hospital with suspected status epilepticus, and 8% of people admitted to hospital with suspected stroke. FND symptoms are usually not transient. A 14-year study of people with functional limb weakness found that 80% still had their symptoms at follow-up. Physical disability and distress are as high as in epilepsy or Parkinson's disease².

FND is a diagnosis of inclusion, with a diagnostic stability similar to other conditions in neurology and psychiatry². People with FND have clinical features that are characteristic of the disorder. Hoover's sign describes impairment of voluntary hip extension in the presence of normal automatic hip extension during contralateral hip flexion. A functional tremor stops or entrains to the rhythm of the examiner in the tremor entrainment test in a way that does not occur in other tremor disorders. People having a functional seizure typically experience a brief prodrome with autonomic arousal and dissociation, followed by an event in which their eyes are closed, and there are either vigorous tremor-like movements, or they fall down and lie still for more than a minute in ways that only occur in this condition.

Injury, pain and infection are common triggers to functional motor and sensory disorders, and appear at least as relevant as adverse experiences². Stressful events, adverse childhood experiences, and psychiatric comorbidity remain important in the story of many people with FND. The frequency of adverse childhood experiences (odds ratio: 3-4) and recent stress (odds ratio: 2-3) is increased, but not that different to many other conditions where they are considered a risk factor and not “the cause”³. There are patients in whom a conversion model still makes sense, but others for whom it is preposterous. The dropping of the requirement for a recent stressful event in the DSM-5, and the change of the name of the condition from “conversion disorder (functional neurological symptom disorder)” in the DSM-5 to “functional neurological symptom disorder (conversion disorder)” in the DSM-5-TR, are in keeping with that. A wider set of hypotheses, considering multiple levels from the neuron to society, is required to make sense of FND.

The “predictive brain” offers a potential solution to puzzling disorders such as phantom limb phenomena, in which strong predictions that a limb “is still there” outweigh sensory input to the contrary. Similarly, in functional paralysis, one hypothesis is that the brain predicts a limb that “is not there” (and thus cannot be moved) so strongly that it outweighs sensory input telling the brain that the limb is normal⁴. The predictive brain builds on older notions of “ideas” or “beliefs” being important in FND, or of conditioned responses to threat, illness or injury that operate below the level of awareness. Neurodevelopmental conditions – including autism spectrum disorder, attention-deficit/hyperactivity disorder, and joint hypermobility – may be more common in people with FND because of an impairment in this predictive and interoceptive machinery.

The first functional neuroimaging study of an FND patient appeared in 1997. The shock news was that FND could be seen in the brain. A number of networks have then been found to be relevant to FND, including those involved in attention, motor control, salience and emotion regulation². Perhaps the most interesting and replicated finding is hypoactivation of the network involved in sense of agency – the parts of the brain that let you know that it is “you” who made a movement – including the right temporoparietal junction. Poor activation of this network is consistent with what we see clinically (“it looks like a voluntary movement”) and what the patient is telling us (“it doesn't feel like under my control”). A diagnostic biomarker for FND may even one day become available⁵. For example, a study of resting state functional imaging was able to classify FND from healthy controls using brain scans alone with an accuracy of 72%⁶.

If one considers FND a disorder of higher voluntary movement, it is hardly surprising that it has often been confused with wilful exaggeration or malingering. But a whole range of clinical and neuroscientific evidence, including geographical and historical consistency as well as remarkable responses to neurophysiological experiments, such as increased accuracy in tests of sensory attenuation, show that feigning offers a poor explanation for the clinical phenomenon of FND⁷.

Treatment for FND reflects this new multidisciplinary approach, starting with an explanation of the disorder that emphasizes diagnosis by inclusion, mechanisms in the brain, but also relevant psychological risk factors when present. FND-focused physiotherapy promotes automatic over voluntary movement, has important differences to physiotherapy for recognized neurological conditions, and shows a lot of promise in randomised trials⁸. FND-focused evidence-based psychological therapy addresses adversity, but also recognizes the physiology of functional seizures and their similarity to panic⁹.

The International FND Society, founded in 2019, embodies this co-operative approach, and is complemented by new patient-led organizations such as FND Hope and FND Action. Together they are defying the dualism which has prevented progress and understanding of this common disabling condition.

功能性神经障碍（FND）在 DSM-5-TR 中被归类为“功能性神经症状障碍（转换障碍）”，在 ICD-11 精神障碍章节中被归类为“分离性神经症状障碍”。

最常做出初步诊断的神经科医生通常几乎不知道这种分类系统，并使用各种术语——例如“功能性”、“心因性”或“非器质性”——来描述瘫痪、震颤、癫痫发作或失明曾经被贴上“癔症”的标签。这种术语的多样性反映了一种在神经病学和精神病学之间来回传递了 150 年的疾病。随着时间的推移，FND 的钟摆在 19 世纪末的脑部疾病和 20 世纪的纯粹心理疾病之间摇摆。今天，FND 研究人员建议钟摆停在中间。反抗 FND 中的二元论可能会导致临床医生、寻求简洁解释理论的人以及分类系统的不一致。但它是了解 FND 和改善全世界数百万 FND 患者护理的重要平台。

对于那些在 DSM-IV 中患有“转换障碍”的人来说，这个想法很简单，液压且令人安慰的弗洛伊德式。某人有压力事件，该事件被压抑并转化为运动或感觉症状，这可能是也可能不是象征性的，也许会减轻压力，有时会达到冷漠的地步。转换障碍通常被认为是一种罕见的疾病，只能通过排除来诊断，并且通常会对心理治疗产生快速反应。历史学家 E. Shorter 宣称，“癔症”已基本消失，取而代之的是疲劳等其他躯体症状¹。

在过去的 20 年里，这种对这种情况的狭隘观点已被证据系统地推翻。FND 是一种常见病症，是神经科医生在门诊和住院中最常见的病症之一，占患者的 5-15% ²。50%的人因疑似癫痫持续状态而被送往医院，8%的人因疑似中风而入院。FND 症状通常不是暂时性的。一项针对功能性肢体无力患者进行的为期 14 年的研究发现，80% 的人在随访时仍然存在症状。身体残疾和痛苦与癫痫或帕金森病一样严重²。

FND 是一种包容性诊断，其诊断稳定性类似于神经病学和精神病学中的其他病症²。FND 患者具有该疾病特有的临床特征。胡佛征描述的是在对侧髋关节屈曲期间存在正常自动髋关节伸展的情况下自愿髋关节伸展受损。在震颤夹带测试中，功能性震颤以其他震颤疾病中不会发生的方式停止或跟随检查者的节奏。患有功能性癫痫的人通常会经历短暂的前驱症状，伴有自主神经觉醒和解离，然后闭上眼睛，要么出现剧烈的震颤样运动，要么倒下并静止不动一分钟以上。仅在这种情况下发生的方式。

受伤、疼痛和感染是功能性运动和感觉障碍的常见诱因，并且至少与不良经历一样相关²。压力事件、不良童年经历和精神合并症在许多 FND 患者的经历中仍然很重要。不良童年经历（比值比：3-4）和近期压力（比值比：2-3）的频率有所增加，但与许多其他情况没有什么不同，这些情况被视为风险因素而不是“原因” ³。对于某些患者来说，转换模型仍然有意义，但对于另一些患者来说，它是荒谬的。DSM-5 中取消了对近期压力事​​件的要求，并将病症名称从 DSM-5 中的“转换障碍（功能性神经症状障碍）”更改为“功能性神经症状障碍（转换障碍）” ）”在 DSM-5-TR 中，与此一致。需要更广泛的假设，考虑从神经元到社会的多个层面，才能理解 FND。

“预测大脑”为诸如幻肢现象等令人费解的疾病提供了潜在的解决方案，在幻肢现象中，对肢体“仍然存在”的强烈预测超过了相反的感觉输入。类似地，在功能性麻痹中，一种假设是大脑预测肢体“不存在”（因此无法移动）的程度如此强烈，以至于它比告诉大脑该肢体正常的感觉输入更重要⁴。预测性大脑建立在 FND 中重要的“想法”或“信念”的旧观念之上，或者是对低于意识水平的威胁、疾病或伤害的条件反应。神经发育疾病——包括自闭症谱系障碍、注意力缺陷/多动障碍和关节过度活动——在 FND 患者中可能更常见，因为这种预测和内感受机制受损。

第一项针对 FND 患者的功能性神经影像学研究出现于 1997 年。令人震惊的消息是，可以在大脑中看到 FND。随后发现许多网络与 FND 相关，包括那些涉及注意力、运动控制、显着性和情绪调节的网络²。也许最有趣和重复的发现是与代理感相关的网络的低激活——大脑中让你知道是“你”做出了动作的部分——包括右侧颞顶交界处。该网络的激活不良与我们在临床上看到的情况（“它看起来像是自愿运动”）以及患者告诉我们的情况（“感觉不像在我的控制之下”）一致。FND 的诊断生物标志物甚至有一天可能会出现⁵。例如，一项静息态功能成像研究能够仅使用脑部扫描将 FND 与健康对照进行分类，准确度为 72% ⁶。

如果人们认为 FND 是一种高级自主运动障碍，那么它经常与故意夸大或装病相混淆就不足为奇了。但一系列的临床和神经科学证据，包括地理和历史的一致性以及对神经生理学实验的显着反应，例如感觉衰减测试准确性的提高，表明假装对 FND 的临床现象提供了一个糟糕的解释⁷。

FND 的治疗反映了这种新的多学科方法，从对疾病的解释开始，强调通过包容性、大脑机制以及存在的相关心理危险因素进行诊断。以 FND 为重点的物理治疗促进自动而非随意运动，与公认的神经系统疾病的物理治疗有重要区别，并且在随机试验中显示出很大的希望⁸。以 FND 为重点的循证心理治疗可以解决逆境，但也认识到功能性癫痫发作的生理学及其与恐慌的相似性⁹。

2019 年成立的国际 FND 协会体现了这种合作方式，并得到 FND Hope 和 FND Action 等新的患者主导组织的补充。他们共同反抗二元论，这种二元论阻碍了对这一常见残疾状况的进步和理解。