FND with sensory symptoms

Written By Tanja Goltnik

Functional neurological disorder with sensory manifestations includes the following sensory symptoms:

  • A sensation of altered perception in a part of the body (more commonly the left) - usually involving the face, arm or leg in various combinations.

  • Sensations, vibrations, lightning, jolts...

  • Double vision, blurred vision

Persistent postural perceptual dizziness

FND with sensory symptoms is also characterised by dizziness, including Persistent Perceptual Postural Dizziness (PPPD)

Dizziness occurring as part of a functional disorder is relatively common and accounts for up to 20% of patients treated in a specialist clinic for vertigo.

Persistent perceptual postural dizziness is a new term that combines previous concepts for functional vertigo, including phobic postural vertigo, visual vertigo and chronic subjective vertigo.

It is a permanent imbalance or dizziness without the rotation that it can provoke:

  • upright posture,

  • active or passive movement,

  • exposure to moving visual stimuli, or,

  • complex visual patterns.

Symptoms persist due to failure of vestibular and cerebral readaptation, often accompanied by secondary anxiety or functional gait disorders (Espay et al., 2018).

Diagnostic criteria for PPPD

A. One or more symptoms of dizziness, unsteadiness or non-spinning vertigo present on most days for at least the last three months. 

  • a) Symptoms last for long periods of time (up to several hours), but their severity waxes and wanes

  • b) Symptoms do not need to be present continuously throughout the day

B. Persistent symptoms occur without specific provocation but are maintained by three factors: upright posture, active or passive movement regardless of direction or position, and exposure to moving visual stimuli and complex visual patterns.

C. The disorder is triggered by events that cause dizziness, unsteadiness, light-headedness, or balance problems, including acute, episodic or chronic vestibular syndromes, other neurological or medical conditions, and psychological distress.

  • a) When a PPPD is triggered by an acute or episodic precipitant, symptoms will settle into the pattern described in criterion A as the precipitant resolves, but may be intermittent at first before consolidating into a persistent course. 

  • b) When PPD is triggered by a chronic precipitant, symptoms develop slowly at first and gradually worsen.

D. Symptoms cause significant distress or functional impairment.

E. Symptoms are not better explained by another disease or disorder.

Visual symptoms

  • Patients with FND often report blurred or even double vision due to "convergence spasm", where one of the eyes is too actively turned inwards towards the nose. While convergence is a normal phenomenon, it is often hyperactive in FND patients, causing problems.

  • Sometimes patients report deterioration or even complete loss of vision in one or both eyes. A diagnosis of functional blindness is made when the pupils of the eyes move and respond normally to light and the areas of the brain responsible for processing visual information are not damaged while the patient reports blindness.

  • Sensitivity to light is characteristic of both sensory functional impairment and those with limb weakness or chronic fatigue syndrome. Often the eye on the same side of the body as the weak limb is sensitive.

  • "Visual snow" is a condition that can be caused by an eye or brain disorder, but can also occur in people who do not have these medical conditions. It manifests itself in the way that when the individual looks at a bright background, they notice a soft static with a sense of things moving, reminiscent of a shaken snow globe. The patient thus sees flickering dots in the field of vision. The "snow" may be coloured, black and white or transparent and may flash. The phenomenon of visual persistence is manifested by patients reporting a persistent visual image in the visual field, which occurs when they stare at an object for a long time or try to follow a fast-moving object with their eyes.

 

    • Hallett, M., Aybek, S., Dworetzky, B. A., McWhirter, L., Staab, J. P., in Stone, J. (2022). Functional neurological disorder: new subtypes and shared mechanisms. The Lancet Neurology, 21(6), 537-550.

    • Popkirov, S., Staab, J. P., and Stone, J. (2018). Persistent postural-perceptual dizziness (PPPD): a common, characteristic and treatable cause of chronic dizziness. Practical neurology, 18(1), 5-13.

    • Ranford, J., MacLean, J., Alluri, P. R., Comeau, O., Godena, E., LaFrance Jr, W. C., ... and Perez, D. L. (2020). Sensory processing difficulties in functional neurological disorder: a possible predisposing vulnerability?. Psychosomatics, 61(4), 343-352.

    • Stone, J., Burton, C., in Carson, A. (2020). Recognising and explaining functional neurological disorder. bmj, 371.

Tanja Goltnik
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