How to Diagnose a Functional Neurological Disorder – Inconsistency and Incongruence

Written by Clay Smith

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Inconsistency and incongruence are two keys to diagnosing a functional neurological disorder. The video demonstration really helps sort this out.

Why does this matter?
Psychogenic spells or movements can be difficult to distinguish from seizure or other movement disorder. Are there clues to help us make the right diagnosis?

Is it functional?
This was a case report of a 67 year old woman with head tremor. She had prior normal imaging and sought a specialist for a second opinion. This video demonstrates two key features of a functional movement disorder (FMD): inconsistency and incongruence. Inconsistency consists of variability in frequency, amplitude, distribution, or severity of the movement; and distractibility, such as suppression or even synchronization of the movement with complex tasks (i.e. finger tapping). Incongruence means the movements are not in keeping with known manifestations of other neurological disorders or are not explainable by known neuroanatomic pathways. Most importantly, gentle and factual, “explanation and reassurance that unrecognised maladaptive thoughts and beliefs can predispose to the development of FMD…increases the possibility of successful resolution of symptoms and concordance with cognitive, physical, and occupational therapies.”

Source
Inconsistency and incongruence: the two diagnostic pillars of functional movement disorder. Lancet. 2022 Jul 23;400(10348):328. doi: 10.1016/S0140-6736(22)01184-9.

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