FND, Until It Was Inoperable Tongue Cancer
FND Nope
Moderator
A 58-year-old woman developed tongue pain, difficulty speaking and severe problems swallowing. She was diagnosed with functional movement disorder. Eleven months after her symptoms began, repeat imaging found squamous-cell carcinoma involving the tongue and tongue base. By then, the tumour was not amenable to surgery and treatment was palliative. The authors do not describe this as unfortunate comorbidity. They describe an organic condition that was wrongly diagnosed as FND.
The case was published by Belén González-Herrero and Francesca Morgante in Movement Disorders Clinical Practice in 2023 under the title Oral Squamous Cell Carcinoma Presenting as a Stiff Tongue. It is worth reading carefully because this was not simply a case where an FND diagnosis happened to precede the discovery of something else. The authors explicitly describe diagnostic bias from the functional diagnosis affecting the interpretation of subsequent evidence. Once the FMD label was attached, evidence was viewed through it.
The patient had previously suffered a subarachnoid haemorrhage caused by an aneurysm in 2005, but had recovered with only mild left-sided hemiparesis. Her new illness began acutely in spring 2021 with pain in her tongue and a sore throat, followed by increasing difficulty speaking, swallowing and moving her tongue. An initial nasendoscopy showed normal palatal function, tongue base and larynx, but she continued to deteriorate. Moving her tongue became increasingly painful, her dysphagia became severe, she developed sialorrhoea, and eventually a nasogastric tube had to be inserted simply to maintain nutrition.
Nine months after symptom onset, investigations including a full blood count, coagulation studies, liver and renal biochemistry, anti-GAD antibodies and cerebrospinal fluid analysis were negative. MRI from the skull base to the clavicle with contrast was reported as normal. Brain MRI showed changes attributed to her previous brain injury, while EMG of the genioglossus and supraglottic muscles was normal. A videofluoroscopic swallowing study, however, showed reduced bolus manipulation caused by reduced lingual coordination and strength.
Despite the progressive pain, severe dysphagia, loss of tongue movement and requirement for tube feeding, the presentation was diagnosed as functional movement disorder, specifically functional tongue dystonia. According to the authors, that diagnosis was based on the acute presentation, the supposedly bizarre or incongruent nature of the syndrome, the fixed posture of the tongue and negative neurological investigations.
That is where this case becomes particularly uncomfortable. The authors state that the videofluoroscopic swallowing study was misinterpreted because of diagnostic bias from the FMD diagnosis. This was not merely a test that failed to find the cancer. The swallowing study had demonstrated impaired lingual coordination and strength, yet its significance was interpreted through an existing functional diagnosis. The label was no longer merely describing the patient's symptoms. It was influencing how subsequent evidence was understood.
“investigations such as video fluoroscopic swallow study were misinterpreted based on the diagnostic bias of FMD.”
When the patient was referred to the movement disorders clinic for review of the functional tongue dystonia diagnosis, the examination did not reveal the sort of variability normally invoked as positive evidence for a functional disorder. She could not mobilise her tongue, had dysarthria and a nasal voice, and distractive manoeuvres produced no change. When the clinicians physically examined the tongue, they found something considerably harder to explain as functional: the tissue was indurated, painful and resistant to passive manipulation. There were no ulcers or leukoplakia to provide an obvious visual warning that this was oral cancer.
MRI of the skull base and neck was repeated 11 months after the symptoms had begun. This time it showed a neoplastic lesion of the tongue and an enlarged lymph node overlying the right sternocleidomastoid. Biopsy provided the answer that the FMD diagnosis had not: moderately to poorly differentiated squamous-cell carcinoma involving the whole anterior tongue and tongue base, staged cT4 N2c M0.
The tumour was not amenable to surgical intervention. The patient was started on palliative treatment.
That outcome matters when discussing diagnostic error. This was not a harmless label that was tidied up at the next appointment. The woman had progressive symptoms for months, required tube feeding, and ultimately had advanced cancer identified after 11 months. The authors note that early diagnosis of oral squamous-cell carcinoma is crucial and that cervical lymph-node metastasis substantially worsens survival and increases the risk of dissemination. A single case report cannot tell us exactly what her outcome would have been had the cancer been recognised earlier, but one fact does not require speculation: by the time it was recognised, surgery was no longer an option.
This case also exposes an awkward gap between how modern FND diagnosis is supposed to work and how it can work in practice. The authors themselves state that FMD diagnosis should rely on demonstrating positive signs. Functional speech disorders are expected to show features such as variability, and functional tongue dystonia may involve fixed deviation or torsion, often alongside other functional movement disorders. Yet the reasons given for this patient's original diagnosis included acute onset, a bizarre or incongruent presentation, fixed posture and negative investigations. When specialists subsequently examined her, her speech disturbance did not change with distraction.
Calling a presentation “bizarre” is not a biomarker. Negative investigations do not make cancer functional. A fixed posture does not belong exclusively to FND. And “incongruency” becomes dangerously circular if an unfamiliar presentation is declared incongruent because clinicians cannot explain it, and that unexplained appearance is then used as evidence that it is functional. In this patient, there was a very concrete reason her tongue was behaving strangely: there was a tumour growing in it.
The authors are refreshingly direct about what happened. They do not rescue the original diagnosis by describing the carcinoma as a newly discovered comorbidity. They write:
“Here, we presented a case of an ‘organic’ condition wrongly diagnosed as a functional neurological disorder (FND).”
That distinction matters. There is an enormous difference between saying that people diagnosed with FND can also develop organic disease and documenting a case in which the supposed functional presentation was the manifestation of the organic disease. The painful fixed tongue, speech problems and dysphagia were not one disease while an unrelated carcinoma quietly existed beside them. The structural neoplastic lesion explained the presentation that had been labelled functional.
Perhaps the most important part of this case is what happened after the label was applied. Diagnostic labels are supposed to organise evidence; they become dangerous when they start overruling it. Here, the authors explicitly identify diagnostic bias from FMD as the reason an investigation was misinterpreted. That is diagnostic overshadowing in remarkably plain language: once clinicians believed the problem was functional, subsequent findings were interpreted in a way that preserved that belief.
The paper ends by arguing for careful clinical examination, an open mind and a broad differential diagnosis when assessing patients diagnosed with FND. That sounds obvious. This case demonstrates why it apparently still needs to be said. A diagnosis should remain vulnerable to contradictory evidence. If progressive deterioration, severe pain, loss of function, tube-feeding-level dysphagia and abnormal findings cannot force reconsideration because everything is being interpreted through an FND framework, the problem is no longer simply that a diagnosis was wrong. The diagnosis has become an obstacle to finding out what is actually wrong.
References
- González-Herrero B, Morgante F. Oral Squamous Cell Carcinoma Presenting as a Stiff Tongue. Movement Disorders Clinical Practice. 2023;10(Suppl 3):S58-S60. Full text at PubMed Central. DOI: 10.1002/mdc3.13769.
- Bagan J, Sarrion G, Jimenez Y. Oral cancer: clinical features. Oral Oncology. 2010;46:414-417. PubMed.
- Bugshan A, Farooq I. Oral squamous cell carcinoma: metastasis, potentially associated malignant disorders, etiology and recent advancements in diagnosis. F1000Research. 2020;9:229. PubMed Central.
- Espay AJ, Aybek S, Carson A, et al. Current Concepts in Diagnosis and Treatment of Functional Neurological Disorders. JAMA Neurology. 2018;75:1132-1141. PubMed Central.