Ophthalmic Delusional Parasitosis
Delusional parasitosis (DP) is a monothematic, somatic delusional disorder. Ophthalmic delusional parasitosis is a subtype of DP in which patients have a fixed belief that parasites are infesting their eyes. These beliefs persist even without evidence to support them. Patients with DP can have fixed beliefs involving any organ, skin being the most common organ involved. Ophthalmic DP presents as a cutaneous delusion such as insects crawling in the eyelids  and less commonly as parasites invading the eye itself. In a broader sense, DP can be classified as primary, secondary (functional), or organic. Primary DP patients present with delusions, but they have no underlying psychiatric or organic condition. Patients with secondary DP have an underlying psychiatric cause for their delusion. Delusions in patients with organic DP, are secondary to other sources such as medical conditions, infectious diseases, or drug abuse.
The incidence of DP is between 1.9 to 27.3 cases per year per 100,000 people. Although DP can present in any age, it most often presents in patients between 50 to 70 years old. Caucasians are more likely to present with these somatic delusions. Women and men present with delusional parasitosis in a ratio of 1:1 under the age of 50, however over the age of 50 women are more likely to present with this condition than men at a ratio of 3:1.
The inciting cause of delusional parasitosis is not always discovered. However, some patients report a preceding stressful life event.
When samples are taken from patient’s skin lesions or excoriations, no true parasites are found.
The pathophysiology of ophthalmic DP and DP is not well understood. However, Huber et al. proposed that deterioration of striatal dopamine transporter (DAT) receptors may play a role. As DAT levels in the striatum diminish, extracellular dopamine levels increase. Some other conditions that diminish the functionality of DAT include cocaine use, alcohol use, schizophrenia, Parkinson’s disease, and Huntington’s disease. All these conditions have been linked as secondary causes of DP with associated decreased DAT function. Atypical antipsychotics, which are dopamine receptor inhibitors, have been utilized as an effective treatment in patients with primary delusional parasitosis. This provides further credence to the theory proposed by Huber et al.
Delusional Parasitosis is a diagnosis of exclusion. Therefore, when clinicians are evaluating a patient complaining of parasitic infection, a thorough work up is advised to rule out other causes for the patient’s symptoms.
Patient history may include exposure to various potential vectors such as other people infected with parasites, house pets, or recent travel to developing countries. Patients can also develop DP after successful treatment for a real parasitic infection in the past.
Patients suffering from tactile hallucinations involving the skin may present with skin excoriations, ulcers, or corneal abrasions from attempting to remove the perceived parasites. They may also have chemical dermatitis from attempts to cleanse the infected skin with home remedies. Slit lamp exam and dilated fundus exam can assess for an inflammatory response or other signs which might indicate real parasitosis or organic DP. Fluorescein is useful for detecting corneal abrasions.
Ophthalmic DP will present primarily in patients as a complaint of parasitic eye infection. Associated symptoms may include pruritis or tactile hallucinations such as a sensation of bugs crawling or biting through the patient’s eyelids. However, clinicians should be aware that the clinical presentation can vary as broadly as the patient’s imagination allows.
Delusional Parasitosis is a somatic subtype of delusional disorder. According to the DSM-5, patients with delusional disorder must:
- Have the persistent delusion for at least 1 month
- Not meet criteria for schizophrenia
- Not have markedly impaired function, odd or bizarre behavior
- Not have prolonged episodes of mania or depression. If episodes exist, they must be brief in comparison to the length of the delusion
- Not have another underlying cause for delusions such as substance use, a medical condition, or other mental illness
An MRI brain and orbits with and without contrast can help assess for abnormal brain lesions or other secondary causes that may lead to the patient’s delusions. Sometimes, physicians may decide to perform mineral oil skin scrapings or biopsy to assess for parasites.
A large part of the work up for patients with delusional parasitosis includes ruling out true microbial infection, and organic causes of delusional parasitosis. Providers can consider ordering: complete blood count with eosinophils, urine drug screen, IgE level, vitamin levels such as B12 and folate, thyroid labs, and testing for microbial organisms such as syphilis, tuberculosis, HIV, or other endemic organisms. 
The differential diagnosis includes real parasitosis, psychiatric illness, substance use, and organic ophthalmic or medical pathology. Patient’s may present with ocular symptoms other than their parasitic delusion such as vision loss or eye pain. Therefore, a full work up is recommended to rule out life or vision threatening causes before diagnosing a patient with ophthalmic delusional parasitosis.
Conditions that can present as organic DP include:
- Medical: hypothyroidism, diabetes, anemia, folate deficiency, and vitamin B12 deficiency.
- Infectious organisms: syphilis, tuberculosis, HIV, leprosy, other endemic organisms
- Substance abuse: cocaine, amphetamines, methylphenidate, pemoline, alcohol
Patients with DP often have other coexisting psychiatric conditions. The Department of Psychiatry at the Mayo Clinic found that out of 54 patients with DP, 74% received additional psychiatric diagnosis and only the remaining 26% had DP alone. Thus, it is advisable to exclude secondary psychiatric causes for patients with ophthalmic DP.
Pavlovsky et al. found only 8% of patients with DP accept referral to psychiatry. Therefore, building trust is a vital component for successful treatment. A multi-disciplinary approach is encouraged for patients with DP involving primary care, psychiatry, infectious disease, dermatology, or ophthalmology in the case of ophthalmic DP. For mild cases of DP, some patients may experience resolution with a strong therapeutic relationship, and symptomatic management for pruritis, pain, or otherwise. For more severe cases of DP, often atypical antipsychotics such as risperidone, olanzapine, and quetiapine are used for psychopharmacological management. Patients often refuse treatment with antipsychotics. Medication adherence is more likely when physicians explain to the patient that they are not prescribing antipsychotics for schizophrenia. Rather, psychiatrists and dermatologists frequently use them to treat distress and the antihistamine component of antipsychotics can help reduce itching.
Medical follow up
Consistent multidisciplinary follow up bolster the patient physician relationship and is advised for successful patient treatment.
Skin excoriations and corneal abrasions have been reported in cases of ophthalmic delusional parasitosis. There is a reported case by Ma et al. of Morgellons disease, a subtype of DP, where enucleation was required after corneal perforation and endophthalmitis.
Patients with DP typically are not markedly impaired. However, the delusions and associated symptoms such as pruritis may prove a persistent nuisance decreasing quality of life. Secondary complications of ophthalmic DP may result such as infected skin excoriations, corneal abrasions, corneal perforation, or endophthalmitis.  Patients generally respond well to atypical antipsychotics with studies showing partial or full remission in 60-100% of patients.
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