Functional Neurological Disorder (FND) and Somatic Symptom Disorder (SSD)

FND and SSD: Real Symptoms, Different Diagnoses

Patients with persistent physical or neurological symptoms unfortunately often feel that they are not being adequately heard or understood. When medical investigations do not provide a complete explanation for the symptoms, this can mistakenly lead to the impression that the symptoms are “psychological,” “imagined,” or “not real.”

That is incorrect. FND and SSD are recognized diagnoses, but they should never be used as convenient diagnostic labels when no other explanation is readily apparent. A diagnosis should be the beginning of explanation, guidance, and treatment—not the end of medical support.

What is FND?

FND stands for Functional Neurological Disorder.

In FND, the way the nervous system functions or controls neurological processes is altered, which can result in genuine neurological symptoms, such as:

• Weakness or paralysis;

• Tremors, jerks, or other movement disorders;

• Problems with walking and balance;

• Altered sensation;

• Problems with speech, vision, or swallowing;

• Functional seizures or attacks;

• Cognitive symptoms.

FND is not diagnosed solely because an MRI, EMG, or blood test does not show an abnormality. The neurologist should identify positive clinical neurological features that are specifically consistent with FND, such as recognizable variability, distractibility, or inconsistency during certain examination tasks. Current Dutch clinical guidelines explicitly emphasize that FND is not a diagnosis of exclusion.

Psychological trauma, stress, an anxiety disorder, or depression may be present and may influence the symptoms, but they are not required for a diagnosis of FND.

What is SSD?

SSD stands for Somatic Symptom Disorder.

In SSD, a patient has one or more physical symptoms that cause significant distress or impairment. In addition, there is a persistent and disproportionate response to these symptoms, for example:

• Constant worrying about one's health;

• Strong fear that a serious illness is present;

• Catastrophic thoughts about physical sensations or symptoms;

• Spending excessive amounts of time and energy on medical checks and monitoring symptoms;

• Severe limitations that are partly maintained by this preoccupation.

The physical symptoms may be medically unexplained, but this is not required. For example, a person with a demonstrable neurological, endocrine, or inflammatory condition may also have SSD. The diagnosis therefore does not depend on whether the symptoms are “real,” but on the extent to which thoughts, emotions, and behaviors related to the symptoms have become disproportionate and disruptive.

Both diagnoses can occur alongside:

• Pain and fatigue;

• Dizziness and cognitive symptoms;

• Limitations in work and daily functioning;

• Sleep disturbances;

• Anxiety, low mood, or sensory overload;

• Previous physical illness, injury, or stressful events.

However, the presence of overlap does not mean that every patient with FND automatically has SSD, or vice versa.

FND and SSD: Key Differences

What Should a Patient Expect After Receiving a Diagnosis?

A carefully established diagnosis should be followed by:

1. A clear and understandable explanation
   The physician should explain which criteria and clinical findings led to the diagnosis.

2. Adequate medical assessment
   Relevant neurological, internal medicine, endocrine, metabolic, toxicological, and medication-related causes should be considered appropriately. Not every conceivable test is always necessary, but the differential diagnosis should be medically sound and carefully considered.

3. Discussion of comorbidities
   FND and SSD do not exclude other conditions. A patient may simultaneously have a neurological, physical, or psychiatric disorder.

4. An individualized treatment plan
   Depending on the symptoms, this may include specialized physiotherapy or exercise therapy, occupational therapy, speech and language therapy, psychoeducation, psychological support, and treatment of coexisting conditions. Dutch guidelines recommend an interdisciplinary approach.

5. Follow-up and reassessment
   When new, progressive, or clearly changing symptoms occur, the patient should be reassessed to determine whether additional diagnostic evaluation is necessary. A previous diagnosis of FND or SSD should never prevent further medical assessment of new symptoms.

What FND and SSD Do Not Mean

These diagnoses do not mean that:

• The patient is making up the symptoms;

• The symptoms are being deliberately produced;

• All symptoms are purely psychological;

• Further medical consideration is no longer necessary;

• Treatment is impossible or unnecessary;

• Every medically unexplained physical symptom is automatically FND or SSD.

A concise key message for patients is:

“Your symptoms are real and deserve serious attention. FND and SSD are different, sometimes overlapping diagnoses. Both require careful assessment, a clear explanation, appropriate treatment, and continued attention to any other underlying medical conditions.”