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Two Women Diagnosed With FND Actually Had POTS — One Was Misdiagnosed Again When She Developed Paralysis

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Two young women arrived at hospital with severe involuntary movements, shaking and other neurological symptoms. Both were diagnosed with functional neurological disorder (FND). Both were subsequently found to have postural orthostatic tachycardia syndrome (POTS), confirmed through tilt-table testing. Their symptoms improved after treatment directed at their underlying conditions. But the most disturbing part of this case series is what happened to one of the patients later: when she developed episodes of weakness and paralysis, another emergency department diagnosed her with FND again. This time, further investigation revealed hypokalemic periodic paralysis, a treatable condition associated with low potassium.

Published in March 2025 in Advanced Neurology, the paper by Alyssa Khoo, Jacob Brik and Anna D. Hohler describes two patients, aged 24 and 18, whose autonomic symptoms and abnormal movements were initially attributed to FND. Both had normal brain and spinal MRI findings and no epileptiform abnormalities on EEG. Neither investigation identified the cause of their symptoms. It was only after specialist neurological assessment, including orthostatic testing, that their POTS diagnoses were established.


Case 1: Diagnosed With FND, Then Diagnosed With FND Again

The first patient was a 24-year-old woman experiencing severe episodes of shaking, dystonia and burning sensations throughout her muscles. Her movements typically occurred in bursts lasting several minutes, separated by approximately 15–20 minutes without shaking. These episodes could continue for hours, sometimes throughout an entire evening, and recur over periods of two to three weeks. They would gradually decrease in severity before disappearing, only to return months later. She could not identify a consistent trigger.

Brain and spinal MRI scans showed no structural abnormalities, while EEG testing found no epileptiform activity. She arrived at the specialist neurology clinic carrying an FND diagnosis. Further examination, however, revealed abnormalities that deserved investigation rather than dismissal: poorly reactive pupils, exaggerated knee reflexes, postural tremor, myoclonic movements affecting her arms, trunk and legs, and severe small-fibre neuropathy.

An initial orthostatic assessment performed at home showed her heart rate increasing from 72 beats per minute while lying down to 126 beats per minute while standing. That was a rise of 54 beats per minute. Subsequent tilt-table testing confirmed POTS, with a heart-rate increase exceeding 30 beats per minute. A 24-hour urine metanephrine test was also negative.

Treatment with pyridostigmine reduced her tremor and myoclonic episodes. Further improvement followed the diagnosis and treatment of additional conditions, including Ehlers–Danlos syndrome, neurogenic bladder and tethered cord syndrome, for which she underwent tethered cord release surgery. Her pyridostigmine dosage was adjusted, and clonazepam was prescribed for use at the onset of symptoms. The frequency of her autonomic episodes decreased.

Then, approximately two and a half years later, she began experiencing episodes of limb weakness and paralysis. She attended another hospital's emergency department, where she was given a new FND diagnosis. Despite her previous experience of being incorrectly diagnosed with FND, another set of neurological symptoms had once again been assigned the same label.

Concerned that the diagnosis was wrong, she returned to her treating neurologist. Blood testing revealed a potassium concentration of 3.3 mmol/L, below the normal range. Further investigation identified hypokalemic periodic paralysis, a condition in which episodes of muscle weakness or paralysis are associated with abnormal potassium regulation.

She was prescribed potassium supplementation, and the episodes of weakness resolved.

"Two and a 1/2 years later, the patient started to experience episodes of limb weakness or paralysis. She presented to an external hospital ED and was diagnosed with a new FND."

— Khoo et al., 2025

That sequence is difficult to ignore. The patient was initially diagnosed with FND when she had autonomic storms and abnormal movements. Investigation subsequently identified POTS and other neurological conditions. When a new symptom emerged years later, another emergency department diagnosed FND again. Her neurologist instead identified a biochemical abnormality, investigated it and diagnosed hypokalemic periodic paralysis. Treatment resolved the weakness episodes. The paper does not provide enough detail to reconstruct the reasoning behind either hospital's FND diagnosis, but the eventual findings demonstrate why new symptoms require proper investigation, regardless of what appears in a patient's previous medical records.


Case 2: Full-Body Jerking, Normal MRI and EEG, Then an FND Diagnosis

The second patient was an 18-year-old woman with a medical history that included Graves' disease treated by thyroidectomy, coeliac disease, migraine and supraventricular tachycardia. She experienced episodes of extremely rapid heart rate, reportedly reaching 140–170 beats per minute even at rest, alongside worsening dizziness and frequent fainting.

She subsequently developed severe involuntary movements. Her first major episode of myoclonus lasted approximately 24 hours, involving substantial full-body twitching. Later episodes typically lasted 20–30 minutes and occurred several times daily, usually in the morning, afternoon and before bedtime. The evening episodes tended to be the most violent. Walking, exercise and physical activity during the day could make them worse.

Immediately before an episode, she experienced intense nausea without vomiting, dizziness and an extreme sensation of cold. Twitching would begin in her right arm or leg before progressing to full-body jerking within two to three minutes. Afterwards, she was exhausted and physically sore.

She underwent emergency assessment and hospital admission. Brain and spinal MRI scans were normal, and continuous EEG monitoring did not identify epileptiform abnormalities. She was subsequently diagnosed with FND.

When she was referred to the specialist neurology team, examination revealed POTS, exaggerated knee reflexes, small-fibre neuropathy and frequent myoclonic movements involving her arms and legs. Tilt-table testing demonstrated a heart-rate increase exceeding 30 beats per minute, confirming POTS in the context of her clinical presentation. Further autonomic evaluation supported the diagnosis.

She was treated with pyridostigmine and diazepam (Valium). According to the authors, her twitching episodes resolved.

The distinction matters. Her normal MRI and EEG did not mean that nothing was wrong, nor did they establish that her movements were functional. Those investigations had failed to identify structural abnormalities or epileptic activity. Autonomic testing, which assessed an entirely different physiological system, provided findings that had not been established during her initial hospital assessment.


What the Authors Found

Both patients had tachycardia, myoclonus and small-fibre neuropathy. Both had been diagnosed with FND in emergency or hospital settings, and both subsequently had POTS confirmed through tilt-table testing. Their abnormal movements improved or resolved following treatment. The authors describe these presentations as POTS-associated autonomic storms and autonomic movement disorders, although the case series is too small to establish how frequently such episodes occur in POTS or whether every movement was directly caused by the autonomic disorder.

The paper also highlights how frequently POTS is initially misunderstood. It cites previous research in which 83% of nearly 700 patients reported receiving a psychiatric diagnosis before their POTS was correctly identified. That figure comes from earlier research and does not represent the rate of FND misdiagnosis specifically. The authors also note that delays in recognising POTS can extend from six months to several years.

Autonomic dysfunction can involve far more than a racing heart. Patients may experience dizziness, fainting, tremor, sweating abnormalities, temperature disturbances, fatigue and other symptoms affecting multiple bodily systems. In these two cases, the most conspicuous symptoms were involuntary movements. The authors argue that clinicians evaluating patients with orthostatic symptoms and myoclonus should consider POTS and perform appropriate cardiovascular and autonomic assessments rather than assuming that unexplained movements are functional.

"Misdiagnosis can delay appropriate management of POTS, highlighting the need for heightened awareness among clinicians when evaluating autonomic symptoms."

— Khoo et al., 2025

There are important limitations. This was a retrospective report involving only two patients, with some information obtained from patient questionnaires. It cannot establish how common POTS-related myoclonus is, prove that POTS caused every movement described, or determine the overall frequency of incorrect FND diagnoses. The patients also had other medical conditions that complicate attributing all their symptoms to POTS alone. Nevertheless, the report documents two individual diagnostic errors and the clinical findings that led to alternative diagnoses and treatment.

The authors conclude that patients presenting with orthostatic symptoms and myoclonus require careful medical histories, orthostatic measurements and appropriate testing, including tilt-table assessment where indicated. Their concern is that attributing neurological symptoms to psychological or functional causes without recognising autonomic disease can delay effective treatment.

The first patient's experience makes the consequences particularly clear. An FND diagnosis did not prevent her from having POTS, severe small-fibre neuropathy, tethered cord syndrome or, later, hypokalemic periodic paralysis. Her second episode of diagnostic mislabelling was followed by a measurable abnormality, a specific diagnosis and resolution of her weakness after treatment. An existing diagnostic label should never substitute for investigating a new neurological symptom.

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