Functional neurological disorder: A practical guide to an elusive Dx
The complexity of this disorder poses a clinical challenge like few others.
PRACTICE RECOMMENDATIONS
› Avoid using stigmatizing terminology (eg, adding the prefix “pseudo” or the adjective “hysterical”) to characterize a suspected functional neurological disorder (FND) or a medically unexplained disorder. C
› Refrain from ordering functional magnetic resonance imaging as part of the routine evaluation of suspected FND. C
› Validate the patient‘s concerns with an appropriate diagnostic label; use layman’s terms to discuss the diagnostic parameters of FND and the cause of symptoms; and emphasize treatment possibilities and plans. C
Strength of recommendation (SOR)
A Good-quality patient-oriented evidence
B Inconsistent or limited-quality patient-oriented evidence
C Consensus, usual practice, opinion, disease-oriented evidence, case series
CASE
The work-up over the next month for Mr. D includes numerous studies, all yielding results that are negative or within normal limits: visual acuity; electrocardiography and an event monitor; laboratory testing (including a complete blood count, comprehensive metabolic panel, thyroid-stimulating hormone, creatine kinase, erythrocyte sedimentation rate, C-reactive protein, vitamin B12, folate, and vitamin D); magnetic resonance imaging of the brain and lumbar spine; lumbar puncture; and electromyography.
The score on the 9-item Patient Health Questionnaire for depression is 4 (severity: “none or minimal”); on the 7-item Generalized Anxiety Disorder scale, 0 (“no anxiety disorder”).
Referral. A neurology work-up of headache, lower extremity weakness, and unsteady gait to address several diagnostic possibilities, including migraine and multiple sclerosis, is within normal limits. A cardiology work-up of palpitations is negative for arrhythmias and other concerning findings.
Mr. D declines psychiatric and psychological evaluations.
Building a differential diagnosisis a formidable task
The differential diagnosis of FND is vast. It includes neurological, physiological, and psychiatric symptoms and disorders; somatization; and malingering (Table 4).6 Any disorder or condition in these areas that is in the differential diagnosis can be precipitated or exacerbated by stress; most, however, do not involve loss of physical function.12 In addition, the diagnosis of an FND does not necessarily exclude an organic disorder.
A patient’s presentation becomes complicated—and more difficult to treat—when functional symptoms and an unrelated underlying or early-stage neurological condition coexist. For example, a patient with epilepsy might also have dissociative seizures atop their organic disorder. Neurological disease is considered a risk factor for an overlying FND—just as the risk of depression or anxiety runs concurrently with other chronic diseases.14
Focus on clinical signs to narrow the differential. A thorough social and medical history and physical examination, as discussed earlier, help narrow the differential diagnosis of organic and medically unexplained disorders. Well-defined imaging or laboratory protocols do not exist to guide physicians to a definitive diagnosis, however.
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