Pernicious Anaemia Mistaken for FND: Paralysis, Urinary Retention and a Missed Diagnosis
FND Nope
Moderator
A 2024 case report published in Cureus describes a 29-year-old woman who was discharged from an emergency department with suspected conversion disorder, now commonly termed Functional Neurological Disorder (FND), despite progressive paralysis and severe urinary retention. Further investigation revealed subacute combined degeneration of the spinal cord caused by vitamin B12 deficiency associated with pernicious anaemia.
Progressive symptoms and an initial functional interpretation
The patient had experienced approximately two weeks of worsening leg weakness and numbness, eventually requiring a wheelchair. Examination documented complete loss of voluntary movement in both lower limbs, absent knee and ankle reflexes, and reduced or absent sensation extending from the upper abdomen downwards. A bladder scan revealed urinary retention exceeding 700 mL.
She had undergone CT and MRI investigations at another hospital approximately two weeks earlier, without an identified explanation. At the second emergency department, a preliminary spinal MRI interpretation was also reported as unremarkable. During the neurological consultation, the patient disclosed significant recent life stressors, including physical and emotional trauma. The consulting team suspected a functional neurological symptom disorder, recommended no further intervention and deferred lumbar puncture. She was subsequently discharged.
The diagnosis changes
Following discharge, a radiology addendum identified abnormalities involving the spinal cord. The patient was contacted and asked to return for further investigation. Dedicated spinal MRI demonstrated signal abnormalities affecting the dorsal columns of the cervical and thoracic spinal cord, consistent with subacute combined degeneration.
Blood investigations subsequently revealed vitamin B12 below 150 pg/mL, elevated methylmalonic acid and homocysteine, and positive intrinsic factor antibodies. These findings supported pernicious anaemia as the underlying cause of her vitamin B12 deficiency and spinal cord injury.
She received vitamin B12 injections and experienced marked improvement in lower limb strength and sensation. Nevertheless, she required discharge to a skilled nursing facility, with a urinary catheter remaining in place until she could void independently. The report does not establish whether she ultimately achieved complete neurological recovery.
When a diagnosis becomes a distraction
What makes this case particularly concerning is how the suspicion of conversion disorder appears to have influenced the decision to stop investigating. The patient's psychosocial history and initially unrevealing imaging were considered sufficiently suggestive of a functional explanation that the consulting team recommended no further intervention, despite substantial objective abnormalities. The report does not document positive functional signs establishing the suspected diagnosis.
The authors acknowledge that anchoring bias may have contributed to the premature diagnosis. The patient's recent physical and emotional trauma featured in the neurological consultation, yet these circumstances did not establish an explanation for her physical findings. Rather than remaining a provisional hypothesis, conversion disorder appears to have become a reason not to pursue further investigation.
The imaging history is equally important. The abnormalities were eventually recognised on radiological review, demonstrating that the initial interpretation had missed existing pathology. The authors also explain that the emergency MRI protocol was less comprehensive than the dedicated spinal study performed later. An initially unremarkable investigation was therefore treated as reassuring before the available evidence had been fully evaluated.
Her initial haemoglobin was also normal, despite the subsequently confirmed vitamin B12 deficiency. This illustrates another limitation of relying on routine investigations to exclude treatable disease. The absence of anaemia did not exclude the neurological consequences of pernicious anaemia.
The consequences of premature closure
The patient was discharged while a treatable cause of spinal cord injury remained unidentified. Although vitamin B12 treatment subsequently produced marked improvement, she still required rehabilitation and bladder catheterisation. The authors emphasise that delayed treatment of subacute combined degeneration can result in irreversible neurological injury.
This was not merely a case in which FND and another condition were found to coexist. The subsequent investigations established a medical explanation for the patient's presentation. Importantly, pernicious anaemia is an autoimmune condition affecting vitamin B12 absorption, rather than a primary neurological disease. Its consequences were neurological, but the underlying cause was systemic.
The case illustrates how a suspected functional diagnosis can become a distraction when it is allowed to interrupt the investigation of unexplained abnormalities. The question is not simply whether the eventual diagnosis was difficult to establish, but whether the initial interpretation was justified by the evidence available at the time. In this instance, the authors themselves identify premature diagnostic closure as a central concern.
References
- Ryan CJ, Tolby N. Subacute Combined Degeneration of the Spine: A Case Study of Delayed Diagnosis in the Emergency Department. Cureus. 2024;16(8):e67764. doi:10.7759/cureus.67764.
- Hemmer B, et al. Subacute combined degeneration: clinical, electrophysiological, and magnetic resonance imaging findings. Journal of Neurology, Neurosurgery & Psychiatry. 1998;65:822–827.
- Burlock B, Williams JP. Recognizing Subacute Combined Degeneration in Patients With Normal Vitamin B12 Levels. Cureus. 2021;13:e15429.
