Functional symptoms; general factors relevant to spotting mimics and chameleons
| Mimics: features of neurological disease that can lead erroneously to a diagnosis of functional symptoms | Diagnostic clues/how not to mess up |
|---|---|
| The presence of psychiatric disorder, especially personality disorder | Detecting psychiatric comorbidity may be useful in treating the patient but should be ignored in making the diagnosis. Focus on the nature of the attack/the physical examination. Are the physical features typical of functional symptoms? |
| Presence of schizophrenia or other psychotic illness | Such patients seldom have functional symptoms. |
| The patient's presenting complaint is of new onset mood or behavioural disturbance. | Patients with functional symptoms rarely complain of significant psychiatric or behavioural symptoms, for example, panic, as their primary, subjective complaint, even if it is clearly present |
| The presence of an obvious life event or stressor | Ignore the presence of recent stress in making the diagnosis, even if this may be relevant for treatment |
| Failure to consider that the patient may have functional symptoms AND a neurological disease | Remember that neurological disease is one of the most powerful risk factors for developing functional symptoms. (eg, epilepsy/non-epileptic attacks, multiple sclerosis/functional weakness, idiopathic intracranial hypertension/functional visual symptoms) |
| Failure to consider that the patient may have functional symptoms AND a progressive neurological disease, which may be too early for you to diagnose (yet) | As above, but in some cases, especially where neuroimaging doesn't help, the disease may only become apparent on follow up (eg, motor neurone disease, Wilson's disease, Alzheimer's disease, myopathy) |
| ‘La belle indifférence’—apparent indifference to disability | This ‘sexy’ French concept is wedded to conversion disorder and is of no diagnostic value, probably occurring more frequently in neurological disease, especially with frontal lobe involvement11 |
| Normal neuroimaging | Many neurological diseases, for instance, epilepsy, motor neurone disease, myopathy, spinocerebellar ataxia have normal brain and spine imaging. Don't rely on it alone to exclude disease |
| Chameleons: features of patients with functional symptoms that can wrongly put you off the diagnosis | |
| The patient is ‘normal’/'nice’/'stoical’/'like me’ | Nice people get functional symptoms too |
| The patient has no ‘form’ that is, previous functional symptoms | Patients can present with dramatic neurological functional symptoms with no prior history |
| The patient has not been stressed | Between 1 in 3 and 1 in 4 patients have no evidence of recent stress |
| The patient is not tired/ only has one symptom | Lack of fatigue or other symptoms should make you think twice about a diagnosis of functional symptoms but monosymptomatic presentations do occur |
| The symptoms came on after injury, minor pathological disease | Commonplace in functional symptoms12 |
| The patient suggests a psychological causation | Around 1 in 4 patients with functional symptoms do think that psychological factors are relevant |
| The patient has an established diagnosis of ‘known epilepsy’, ‘known MS’ | Always question other people's diagnoses (and your own!) |
| The patient is too old | Older patients with functional symptoms often have health anxiety and comorbid disease and are probably under-recognised8 |
| Incidental abnormalities on MRI (eg, enlarged perivascular space, Chiari malformation), EEG, serology or other tests | Do not assume that all structural abnormalities are relevant |