What is formication

Formication is sensations like insects biting and crawling over your skin without the believe that they are caused by organisms. Patients with formication experience crawling, biting and stinging sensations of the skin 1). Formication is a type of tactile hallucination. Formication has many causes include various medical conditions, altitude sickness, prescription drug side effects, and drug withdrawal. Formication is often associated with delusions of parasitosis, where patients have a fixed, false belief that they are infested with parasites or other organisms 2). However, unlike delusions of parasitosis patients, those with formication have no firm belief that their symptoms are due to a parasite or infestation 3). Some patients explicitly state that they do not believe the sensations are due to a living thing, while other patients have considered an infestation as a possible cause for the symptoms but are not convinced that this is the case. By definition, when patients are not certain whether they have an infestation or if they believe they do not have an infestation, these patients are not psychotic as they do not have a fixed and absolute delusional ideation. Formication by itself can still warrant the use of drug therapy because it can be debilitating. Formication may be idiopathic or secondary to an underlying neurological diagnosis such as multiple sclerosis.

What causes formication

Causes of formication include normal states such as onset of menopause (i.e. hormone withdrawal). Other causes are medical conditions such as pesticide exposure 4), mercury poisoning, diabetic neuropathy, skin cancer, syphilis, vitamin B12 deficiency, multiple sclerosis, cerebrovascular disease, Lyme disease or herpes zoster (shingles) 5). Formication can be a result of stimulant intoxication (e.g. methamphetamines, cocaine) 6), 7) or withdrawal from cocaine, amphetamines or alcohol withdrawal in alcoholics (i.e. delirium tremens), and is often accompanied by visual hallucinations of insects (formicanopia) 8). It can also occur as a symptom of benzodiazepine withdrawal, withdrawal from medication such as SSRI/SNRI antidepressants and tramadol; and as a side effect of opioid analgesics.

In studies of patients admitted to drug treatment facilities for methamphetamine abuse, approximately 40% of the patients report having had formication 9); If the patients had every suffered from psychosis, then the percentage of persons experiencing formication rose to 70% 10).

How to treat formication

The treatment for formication involves treating the underlying causes of formication. If, for example, it is being caused by medication, a change of medication can be used to resolve the formication. Medications and medical procedures used to manage the itching and tingling associated with neuropathies can also be employed to treat formication.

Patients with delusions of parasitosis should be treated by two professionals – a dermatologist as well as a psychiatrist 11). Generally, however, these patients refuse to see a mental health professional because they do not recognize that the underlying cause of their symptoms is of a psychiatric nature. Therefore, dermatologists need to know how to effectively treat formication patients without the assistance of a mental health professional or else a large proportion of these patients will never be effectively treated 12).

The first and most critical step toward assisting these patients effectively is taking the time to develop a strong physician–patient therapeutic alliance 13). Without a strong alliance, delusions of parasitosis patients are unlikely to be compliant in taking antipsychotic medications. This may include performing laboratory tests, cultures or examining patient specimen samples.

Historically, the pharmacologic treatment of choice for delusions of parasitosis is an antipsychotic medication called pimozide (Orap®) 14). Non-pharmacologic interventions have limited use for formication patients because the underlying disorder is psychosis. By definition, psychotic patients cannot be talked out of a delusion, or else they would not have a delusional disorder in the first place. Pimozide can be prescribed with a starting dose of as low as half a tablet or 0.5 mg daily. As there is a possibility of extrapyramidal side-effects, including restlessness and stiffness, the starting dose of pimozide should be low. These side-effects can generally be controlled with diphenhydramine (Benadryl®) 25-50 mg every 4-6 hours as needed or benztropine (Cogentin®) 1-2 mg four times daily as needed. The dosage can be gradually increased until the optimal response is obtained. It can be increased by as little as half a tablet or 0.5 mg increments as slowly as on a biweekly basis. Clinical improvement is typically evident when the patient reaches the dose of 3-5 mg of pimozide daily. Before starting pimozide, the clinician should consider checking an electrocardiogram (ECG) to ensure the patient does not have an arrhythmia or increased QT interval. Even for those patients without a history of cardiac conduction abnormalities, it may still be advisable to obtain pre-treatment ECG.

Once the optimal dosage of pimozide is found, it should be maintained for 1-3 months. During this period, if the patient continues to show improvement, whereby the delusions of parasitosis becomes minimal or non-existent, the dosage can then be gradually decreased by 1 mg every 2-4 weeks to see whether the patient can be tapered off the pimozide. Once pimozide is discontinued, patients often feel that the pimozide destroyed the organisms or that the organisms are no longer causing bothersome symptoms. Except in a very rare occasion, the patient remains convinced that he or she did have an infestation. Even though these patients almost never actually change their mind, a successful treatment with pimozide typically results in a good outcome, whereby the patient’s continued belief that he or she did have an infestation no longer matters as the patient is now convinced that the organism has been destroyed. The risk of tardive dyskinesia exists, but the actual occurrence is very rare due to low dosage and short-term use.

If extrapyramidal side-effects occur, and do not resolve with benztropine or diphenhydramine, patients may be switched to atypical antipsychotics such as risperidone (Risperdal®), olanzapine (Zyprexa®), quetiapine (Seroquel®), ziprasidone (Geodon®) and aripiprazole (Abilify®). Prior to starting these medications, it is crucial to check a complete blood count (CBC) at baseline, 1 month, 6 months and 1 year in order to monitor for bone marrow suppression. Following this timetable, patients should also have fasting lipids, fasting glucose, glycated hemoglobin (HBA1C), weight and body mass index monitored for possible metabolic complications such as hyperlipidemia, hyperglycemia and excessive weight gain.

Risperidone (Risperdal®) is the preferred alternative to pimozide for delusions of parasitosis 15). It is often initiated at 0.5 mg at night, as it can be sedating. Then, the medication can be up-titrated by 0.5 mg increments every 2-4 weeks to a therapeutic range, or approximately 1-3 mg each night. While on the medication, it is important to regularly monitor for elevated prolactin levels, which can lead to galactorrhea, increased risk of fractures, low bone mineral density and sexual dysfunction.

The second preferred option is olanzapine (Zyprexa®) 16). Olanzapine can be started at 2.5 mg daily, and slowly titrated to a therapeutic dose of 5-10 mg daily. Patients can develop metabolic syndrome and, therefore, should be monitored regularly for weight gain, HbA1C, fasting glucose and fasting lipids.

Many cases have reported that quetiapine (Seroquel®) is effective for delusions of parasitosis 17). It may be initiated at low doses of 12.5 mg in the evening, and slowly titrated up to 200 mg each night. It is often sedating, but this side-effect is fleeting and typically resolves after 3-7 days. Finally, it is important to monitor for orthostatic hypotension while taking quetiapine.

Case reports have also shown the effectiveness of ziprasidone (Geodon®) in delusions of parasitosis 18). It can be started at 5-10 mg twice daily, and slowly titrated up to a therapeutic dose of 20-50 mg twice daily. It is often recommended that ziprasidone be taken with meals as it has lipid-absorptive properties. Anxiety and restlessness have been reported after taking this medication.

Aripiprazole (Abilify®) has been shown to be effective in delusions of parasitosis through case reports 19). It can be started at 2-5 mg daily, and slowly titrated to a therapeutic dose of 10-15 mg daily. As it can be a stimulant, aripiprazole is typically taken during the morning. It is important to monitor for weight gain as well as the side-effects of restlessness, anxiety, weakness and headache.

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