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 的精神障碍章节中被归类为“分离性神经症状障碍”。

神经科医生最常做出初步诊断，通常几乎不知道这样的分类系统，并使用各种术语——例如“功能性”、“心因性”或“非器质性”——来描述曾经被贴上“歇斯底里”标签的瘫痪、震颤、癫痫发作或失明的症状。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 钟摆在 19 世纪末的脑部疾病和 20 世纪的纯粹心理状况之间摆动。今天，FND 研究人员建议钟摆位于中间。在 FND 中违背二元论可能会导致临床医生、寻求整洁解释理论的人和分类系统的不和谐。但它是了解 FND 和改善对全球数百万 FND 患者护理的重要平台。

对于那些在 DSM-IV 中与“转换障碍”一起长大的人来说，这个想法很简单，很流畅，而且很弗洛伊德式。某人有一个压力事件，它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，也许减轻了压力，有时达到美女冷漠的程度。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，并且通常对心理治疗反应迅速。历史学家 E. Shorter 宣称，“歇斯底里”在很大程度上已经消失，取而代之的是其他躯体症状，例如疲劳¹。

在过去的 20 年里，这种对病情的狭隘看法已被证据系统地瓦解。FND 是一种常见病症，是神经科医生在门诊和住院环境中最常见的病症之一，占患者的 5-15%²。它占因疑似癫痫持续状态紧急入院的患者的 50%，占因疑似中风入院的患者的 8%。FND 症状通常不是一过性的。一项针对功能性肢体无力患者的 14 年研究发现，80% 的患者在随访时仍有症状。身体残疾和痛苦与癫痫或帕金森病一样严重²。

FND 是一种包含的诊断，其诊断稳定性类似于神经病学和精神病学² 中的其他疾病。FND 患者具有该疾病的特征性临床特征。Hoover 征描述了在对侧髋关节屈曲期间存在正常的自动髋关节伸展的情况下，自主髋关节伸展受损。功能性震颤会停止或夹带检查者在震颤夹带试验中的节奏，这在其他震颤障碍中不会发生。患有功能性癫痫发作的人通常会经历一个短暂的前驱症状，伴有自主神经唤醒和分离，然后是闭上眼睛的事件，要么有剧烈的震颤样运动，要么他们跌倒并静止不动超过一分钟，这种方式只发生在这种情况下。

受伤、疼痛和感染是功能性运动和感觉障碍的常见触发因素，并且看起来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 患者的故事中仍然很重要。童年时期不良经历（比值比：3-4）和近期压力（比值比：2-3）的频率增加，但与许多其他情况没有太大区别，在这两种情况下，它们被认为是风险因素而不是“原因”³。有些患者认为转换模型仍然有意义，但对另一些患者来说它是荒谬的。DSM-5 中取消了对近期应激事件的要求，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 DSM-5-TR 中的“功能性神经症状障碍（转换障碍）”，这与此一致。考虑到从神经元到社会的多个层次，需要一套更广泛的假设来理解 FND。

“预测性大脑”为幻肢现象等令人费解的疾病提供了一种潜在的解决方案，其中对肢体“仍然存在”的强烈预测超过了相反的感觉输入。同样，在功能性麻痹中，一种假设是大脑对“不存在”（因此无法移动）的肢体的预测如此强烈，以至于它超过了告诉大脑该肢体是正常的⁴ 感觉输入。预测性大脑建立在旧的概念之上，即 “想法 ”或 “信念 ”在 FND 中很重要，或者对威胁、疾病或伤害的条件反应，这些反应在意识水平以下运作。神经发育状况（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。

FND 患者的第一次功能性神经影像学研究出现在 1997 年。令人震惊的消息是，可以在大脑中看到 FND。然后发现许多网络与 FND 相关，包括涉及注意力、运动控制、显著性和情绪调节^{的网络 2}。也许最有趣和最可复制的发现是涉及代理感的网络的低激活——大脑中让你知道是“你”做了一个动作的部分——包括正确的颞顶交界处。这个网络激活不良与我们临床上看到的（“它看起来像一个自愿的运动”）和患者告诉我们的（“感觉不受我的控制”）是一致的。FND 的诊断生物标志物甚至可能在某一天变得可用⁵.例如，一项关于静息态功能成像的研究能够单独使用脑部扫描将 FND 与健康对照者进行分类，准确率为 72%⁶。

如果一个人认为 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也就不足为奇了。但是一系列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 FND⁷ 的临床现象提供了糟糕的解释。

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，强调通过纳入、大脑机制以及相关的心理风险因素进行诊断。以 FND 为重点的物理疗法促进自动运动而不是自主运动，与针对公认的神经系统疾病的物理疗法有重要区别，并且在随机试验中显示出很大的前景⁸。以 FND 为重点的循证心理疗法解决了逆境，但也认识到功能性癫痫发作的生理学及其与恐慌⁹ 的相似性。

成立于 2019 年的国际 FND 协会体现了这种合作方式，并得到了 FND Hope 和 FND Action 等新的患者主导组织的补充。他们共同挑战阻碍了对这种常见残疾状况的进步和理解的二元论。