Differentials
Illness anxiety disorder
SIGNS / SYMPTOMS
At least 6 months of preoccupation with having or acquiring a serious disease, often based on misinterpretation of bodily symptoms. Although the fear usually persists despite reassurance, these patients either seek reassurance or avoid medical care, whereas those with somatic symptom disorder seek confirmation of illness. Unlike somatic symptom disorder, somatic symptoms are either not present or only mild in intensity. If another medical condition (or risk for a medical condition) is present, the preoccupation with illness is excessive or disproportionate.
INVESTIGATIONS
Structured clinical interview. The Health Anxiety Inventory.[93]
Body dysmorphic disorder
SIGNS / SYMPTOMS
Preoccupation with physical appearance; patients have strong belief that they have an abnormality or defect in appearance about which they are overly self-conscious; often undergo cosmetic procedures with little satisfaction.
INVESTIGATIONS
Structured clinical interview.
Factitious disorder
SIGNS / SYMPTOMS
Patients feign, deliberately produce, or exaggerate their physical symptoms. It may be with the intent to assume the sick role, but the deceptive behaviour is evident even in the absence of external rewards.
Malingering
SIGNS / SYMPTOMS
Patients consciously fabricate or exaggerate the symptoms of mental or physical disorders for secondary gain (e.g., financial compensation, avoiding work or military service, obtaining drugs, getting out of going to school, or attracting attention or sympathy). Unlike patients with somatic symptom and related disorders, they often lack cooperation during diagnostic evaluation. Often associated with antisocial personality disorder.
INVESTIGATIONS
Structured clinical interview. Neuropsychological battery such as computerised assessment of response bias and test of memory malingering. There is significant discrepancy between claimed illness and appearance or behaviour outside of physician's surgery.
Dissociative disorder
SIGNS / SYMPTOMS
Although functional neurological disorder can be conceptualised as a form of dissociation, a dissociative disorder can also include periods of detachment from self or surroundings experienced as 'unreal' or 'outside' of self; periods of time that the patient cannot recall; fugue states; or ≥2 distinct personality states.
INVESTIGATIONS
Structured clinical interview.
Major depressive disorder
SIGNS / SYMPTOMS
Depression often presents with somatic complaints, particularly in cultures in which mental illness carries a strong stigma. Typical symptoms include dizziness, fatigue, pain, and feelings of inner pressure. A depressive disorder should be considered if these somatic complaints are in the context of other symptoms of depression such as sleep and appetite disturbance, poor concentration, lack of interest or motivation, and/or thoughts of suicide. Psychotic depression can also include somatic delusions, which should be differentiated from a primary somatic symptom disorder.
INVESTIGATIONS
Structured clinical interview.
Epilepsy
SIGNS / SYMPTOMS
Positive family history. Previous central nervous system infection or trauma. Prior seizure events. Focal neurological symptoms (before or after seizure). Focal neurological deficit. Premonitory sensation or experience. Temporary hemiparesis. Temporary aphasia.
INVESTIGATIONS
Electroencephalogram (EEG): epileptiform activity or focal, localising abnormality.
CT/MRI: may reveal evidence of a structural lesion or other process that has caused the seizure. Note that functional seizures and epilepsy may co-exist in some people.[10]
Spasmodic dysphonia
SIGNS / SYMPTOMS
Strained or breathy speech. Vocal fatigue.
INVESTIGATIONS
Fibre-optic laryngoscopy: abnormal delay between onset of electrical and acoustic activity.
Stroboscopy: involuntary vocal fold adduction or abduction during connected speech.
Dystonia
SIGNS / SYMPTOMS
Functional dystonia, in contrast to other types of dystonia, usually presents as a fixed position, usually a clenched fist or inverted ankle (whereas other types of dystonia are usually mobile). Functional facial dystonia usually presents with episodic contraction of the platysma or orbicularis.[66]
INVESTIGATIONS
Levodopa responsiveness: positive if clinical improvement.
Parkinson's disease
SIGNS / SYMPTOMS
Manifestations of functional parkinsonism may be similar to those of Parkinson's disease, with rest tremor, bradykinesia, rigidity, and postural instability. However, there may be associated features suggesting a functional origin, including the presence of other functional signs and symptoms.[96]
Note that Parkinson's disease and functional neurological disease may co-exist in some people.[8]
INVESTIGATIONS
Dopaminergic agent trial: improvement in symptoms.
Olfactory testing: hyposmia or anosmia.
Electrophysiological testing: may distinguish between functional tremor and Parkinson's disease tremor.
FP-CIT single photon emission computed tomography: may show loss of dopamine transporters in Parkinson's disease.
Parkinsonism
SIGNS / SYMPTOMS
Manifestations of functional parkinsonism may be similar to those of non-functional parkinsonism, with rest tremor, bradykinesia, rigidity, and postural instability. However, there may be associated features suggesting a functional origin, including the presence of other functional signs and symptoms.[96]
INVESTIGATIONS
Improvement with removal of medication with potential extrapyramidal adverse effects.
Multiple sclerosis
SIGNS / SYMPTOMS
Visual disturbance in one eye. Peculiar sensory phenomena. Foot dragging or slapping. Leg cramping. Fatigue. Urinary frequency.
Note that multiple sclerosis and functional neurological disorder may co-exist in some people.[9]
INVESTIGATIONS
MRI brain: hyperintensities in the periventricular white matter, most-sensitive images are sagittal fluid-attenuated inversion recovery (FLAIR).
MRI spinal cord: demyelinating lesions in the spinal cord, particularly the cervical spinal cord; detection of alternate diagnosis, such as cervical spondylosis.
Stroke
SIGNS / SYMPTOMS
Sudden onset of unilateral numbness, weakness, or confusion or visual changes.
INVESTIGATIONS
MRI/CT brain: ischaemic or haemorrhagic changes.
Dementia
SIGNS / SYMPTOMS
Progressive loss of cognitive functioning, often in multiple domains, which can impair daily activities of living. Occasionally, patients with dementia can also have somatic delusions.
INVESTIGATIONS
Neuropsychometric testing: dementia-related cognitive changes, and cognitive dysfunction patterns.
CT/MRI brain: cerebrovascular lesion with vascular dementia.
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