Functional Neurological Symptom Disorder Obscured by Incomplete Diagnostic Communication: A Case Report.

Functional neurological disorder (FND) is a diagnosis grounded in positive clinical signs, yet it remains vulnerable to underdocumentation and incomplete communication across care transitions, particularly when it is suspected but not formally recorded. In this case, a 24-year-old woman with a history of major trauma (three gunshot wounds sustained four years earlier) presented with sudden-onset left lower extremity (LLE) weakness, pain, and tingling coinciding with the anniversary month of her injury. Extensive neuroimaging and serologic workup were unrevealing aside from an incidental disc protrusion and elevated angiotensin-converting enzyme (ACE) titers. Due to the presence of localized lower extremity plegia and anesthesia in the absence of structural pathology on neuroimaging, the patient was empirically treated for suspected autoimmune plexopathy with high-dose methylprednisolone, intravenous immunoglobulin (IVIG), and plasmapheresis without sustained benefit. On transfer to a tertiary center, examination revealed fluctuating strength and non-anatomic sensory loss; electromyography was inconclusive. The patient was discharged with a diagnosis of "suspected plexopathy of the lumbosacral plexus," though peer-to-peer consultation later revealed that the tertiary team's leading differential had, in fact, been FND, a suspicion that was never formally documented. On admission to acute inpatient rehabilitation, neuropsychological evaluation suggested a history of post-traumatic stress disorder (PTSD) and a positive Hoover's sign supporting functional weakness. A diagnosis of FND was established, taking into account the entire clinical assessment, including history, physical examination, and multidisciplinary evaluation. This case demonstrates that a functional diagnosis privately suspected but not formally documented can be effectively lost at a transition of care, exposing the patient to repeated invasive empiric therapy and diagnostic delay. Formally documenting FND as an active differential diagnosis and delivering an early, transparent, biopsychosocially framed explanation to the patient may reduce iatrogenic harm and support engagement in rehabilitation.