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What is Functional Neurological Disorder (FND)? What symptoms and manifestations can FND give?

fnd diagnosis fnd meaning fnd symptoms functional neurological disorders (fnd) Oct 17, 2021

Functional Neurological Disorder (FND), although a very distinct neurological problem, is also popularly known by many other names, some of which I have listed below. The variability in nomenclature through time and currently, is just one factor contributing to the misunderstandings around this common neurological illness. I will be sharing during upcoming blog posts and informative videos, the history behind its terminology, together with the pros and cons of using modern vs old terminology.

Some of the terms used to describe Functional Neurological Disorder (FND) are:

  • Functional Neurological Symptom Disorder
  • Functional Neurological Deficit
  • Functional Nerve Disorder
  • Functional Brain Disorder
  • Functional Neurological Dysfunction
  • Functional Disorders of The Nervous System
  • FND Illness
  • FND Syndrome
  • FND Condition
  • Psychosomatic Disorder
  • Psychosomatic Illness
  • Conversion Disorder
  • Functional Conversion Disorder
  • Functional Neurological Conversion Disorder

Functional Neurological Disorder (FND), as the name says it, represents a group of conditions, illnesses and symptoms that appear due to a disruption in the normal functioning of the nervous system. The human nervous system is very complex and widespread, going from the brain (the conscious and subconscious mind, the automatic or autonomic centers, the various lobes involved in the perception and processing of hearing, vision, memory, movements, speech, just to name a few), continuing downwards towards the spinal cord, from which many nerves exit and proceed towards the skin, all our perception organs, internal organs, muscles, joints, tendons, etc.

The nervous system then, innervates most of the structures and tissues of the body, participating in the control of everything we think, do, and perceive, consciously and subconsciously, for example, our movements, our energy level, our thoughts, our feelings, our sensations, the way we talk, our sight, our sense of smell. The nervous system in some way, contributes to everything the body does, is tightly linked to our physical body and its functions, all our emotions, our beliefs, desires, and all these processes are closely linked to what takes place in the environment that surrounds us. Having understood this, you could imagine that FND could manifest in a myriad of ways.

Below you have a list with the major categories of FND symptoms. This is a screenshot from Cerner, one of the electronic medical record systems, demonstrating how physicians can code for the various subtypes in the International Classification of Diseases 10th Revision (ICD-10).  

Below, I have detailed a more comprehensive list of the various Functional Neurological Disorders subtypes:

  • Functional limb weakness & paralysis
  • Functional sensory symptoms
  • Functional tremor, dystonia, jerks, tics, paroxysmal movement disorders, parkinsonism
  • Functional gait disorders
  • Functional eye movement disorder
  • Functional facial and tongue movement disorders
  • Functional speech and voice disorders
  • Functional disorders of swallowing
  • Non-epileptic seizures (objective & subjective symptoms)
  • Functional visual loss
  • Functional auditory disorders
  • Functional memory disorder
  • Functional (dissociative) retrograde amnesia
  • Functional dizziness
  • Functional urologic symptoms
  • Functional coma
  • Pediatric FNDs

Functional Neurological Disorders, therefore, could manifest with weakness, paralysis, fatigue, lack of energy, any variety of symptoms affecting the sensations, such as numbness, tingling, pricking, pressure, or any perception that feels abnormal. It can also affect the coordination, cause tremors, tics, and abnormal movements like Parkinson's disease. FND could also affect walking and be classified as functional gait disturbance. Non-epileptic seizures can produce shakes or other manifestations that can look like seizures; episodes with visible signs such as passing out, or more internal, subjective sensations, such as feeling like a seizure is about to happen, inner trembling, jitteriness and other indicators imperceptible by the doctor.

Functional Neurological Disorders can also cause visual disturbances, affect the eye movements, the facial movements, tongue movements, hearing, speech, voice quality and swallowing. At other times it could cause persistent memory issues, or it can be more sporadic, like having occasional amnesia, memory loss, attention, or concentration problems. It can also cause dizziness, affect the urinary system, and even impact children, which is described as “Pediatric FND”. Rarely FND can be so severe, that it can lead patients to coma, although thankfully, this is uncommonly seen.

So, FND is a disorder, a problem in the way one part, or various parts of the nervous system are functioning, and because of this, the symptoms or manifestations vary tremendously, depending on the specific section(s) of the nervous system that are out of balance. All the symptoms I mentioned above, are just examples; in real life we can see many more expressions and even combination of various symptoms and signs in the same person. It is important to remember, that Functional Neurological Disorders are also characterized by frequent fluctuation in the severity, appearance, and type of discomfort.

To complicate matters, many organic diseases can also cause similar symptoms, so, even when patients have a diagnosis of Functional Neurological Disorders, they should not assume that all their discomfort is due to FND, and it is vital to keep an open, and up to date communication with the health care professional treating the condition.

What is the difference between a Functional, and an Organic Neurological disease?

A Functional Neurological Disease is a problem that affects the functioning of the nervous system, AND it does NOT affect the anatomy or the structure of the organs and tissues of the nervous system. This is precisely one of the reasons why Functional Illnesses are so hard to diagnose; because when doctors perform examinations looking at markers of tissue and organ damage such as blood tests, X ray (XR), Magnetic Resonance Imaging (MRI), Computer Tomography (CT), Ultrasound (US), Electromyography (EMG), among others, the results are normal. Besides, most of the exams we have available in clinical practice investigate the structure, the anatomy of organs, the presence of inflammatory or tumor markers, clues of immune mediated diseases, problems in the blood flow, etc, and these are all normal. Tests such as Electroencephalography (EEG), analyze the electrical activity of the brain, but mainly identifies electrical abnormalities that have an organic or genetic origin, that is why this test is also normal.

In research and clinical trials settings, there is the ability to do more sophisticated examinations such as functional MRI (fMRI) and positron emission tomography (PET), which look at the function, metabolic and physiologic processes of the nervous system, and these have revealed abnormalities, for example; one study revealed that patients with weakness and trouble moving had temporary reduced activity in the basal ganglia, which are deep brain structures involved in the realization of normal movements. The abnormalities originally seen in the images improved when the patient’s symptoms subsided (Vuilleumier et al 2001, Schrag et al 2013).

Thanks to this modern technology, and to the research taking place using functional brain imaging, scientists, and the medical community, are getting to understand better Functional Neurological Disorders, why and how it happens, but regretfully these tests are not readily available in most clinical practice, nor they are easily covered by insurance. 

It is paramount then, that we continue to inform ourselves, understand our bodies, our minds and their interconnectedness with our emotions, our spirituality, and the environment where we are submerged, because only by doing so, we will be able to re-balance our nervous system and recover our health, in this age of ongoing research. 


As always,

At your service,

Yadira Velazquez, MD.

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