Ophthalmic Delusional Parasitosis

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Article initiated by:

Noor Laylani, M.D.

All contributors:

Andrew Go Lee, MD, Brandon Martin, B.S., Caitlin Makenzie Hackl, Nagham Al-Zubidi, MD, Pamela Davila-Siliezar, MD, Calvin W Wong, Osama Al Deyabat, MBBS, Nagham Al-Zubidi, MD, Noor Laylani, M.D., Osama Al Deyabat, MBBS, Sanjana Jaiswal

Assigned editor:

Osama Al Deyabat, MBBS

Review:

Assigned status Up to Date

 by Osama Al Deyabat, MBBS on September 18, 2024.

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Disease Entity

Disease

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 without evidence to support them, classifying them as delusions. 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 without underlying psychiatric or organic conditions. Patients with secondary DP have an underlying psychiatric cause for their delusion such as schizophrenia. Delusions in patients with organic DP, are secondary to other sources such as medical conditions, infectious diseases, drug abuse, or withdrawal.

Epidemiology

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.

Etiology

The inciting cause of delusional parasitosis is not always discovered. However, some patients report a preceding stressful life event.

General Pathology

When samples are taken from patient’s skin lesions or excoriations, no true parasites are found. Skin scraping or biopsy, where appropriate, is therefore important in ruling out true parasites such as scabies, worms, dermatophytes, and insects.

Pathophysiology

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.

History

The history taking for a case of suspected DP should begin with directed questioning regarding exposures, comorbidities, prescription medications, recreational drug use, and onset of complaint. 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 of a true parasitic infection in the past.

Physical examination

Upon physical examination, patients with Ophthalmic DP 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, of which acid, alkali, and peroxide are the most common. External upper and lower eyelid examination, slit lamp examination, and dilated fundus examination can assess for local inflammatory response, systemic disease causing organic DP, or other signs which may indicate real parasitosis or organic DP. Fluorescein staining with cobalt blue illumination is useful for detecting any corneal abrasions in these patients. Further, application of topical proparacaine may be helpful in ruling out primary delusional parasitosis, as the anesthetic agent should improve itching or unpleasant sensations in true parasitosis or infection of the eyelid or conjunctiva. Last, tarsal eversion and careful examination of the eyelid margin, eyelash bases, and superior and inferior fornices should be done in a patient complaining of parasitic infection of the eye.

Symptoms

Ophthalmic DP presents primarily as a complaint of parasitic eye infection. Associated symptoms may include pruritus or tactile hallucinations such as a sensation of bugs crawling or biting through the patient’s eyelids. Additional, irritation, redness, or tearing may be present due to excessive self-excoriation or manipulation. However, clinicians should be aware that the clinical presentation can vary as broadly as the patient’s imagination allows. As described previously, application of topical proparacaine may be helpful in characterizing the nature of the delusional parasitosis.

Clinical diagnosis

Delusional Parasitosis is a somatic subtype of delusional disorder. According to the DSM-5, patients with delusional disorder must:

1. Have the persistent delusion for at least 1 month
2. Not meet criteria for schizophrenia
3. Not have markedly impaired function, odd or bizarre behavior
4. Not have prolonged episodes of mania or depression. If episodes exist, they must be brief in comparison to the length of the delusion
5. Not have another underlying cause for delusions such as substance use, a medical condition, or other mental illness

Clinicians should have a degree of clinical suspicion especially when patients spontaneously complain of worm, parasite, or insect infestation. A thorough workup is nevertheless necessary to rule out other causes for the patient’s symptoms.

Of note, delusional parasitosis by proxy should also be considered in certain patient populations (i.e., pediatric, dementia, elderly, intellectually disabled). In this case, patients may present with irritant dermatitis or conjunctivitis due to unnecessary treatments or home remedies. These patients’ caretakers should be evaluated for the above criteria.

Diagnostic procedures

An MRI brain and orbits with and without contrast can help assess for abnormal brain lesions or other secondary causes of the patient’s delusions. Sometimes, physicians may decide to perform mineral oil skin scrapings or biopsy to assess for parasites.

Laboratory test

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 . After extensive workup has returned negative for treatable causes, a diagnosis of primary delusional parasitosis may be made in the absence of psychiatric illness.

Differential diagnosis

The differential diagnosis of ophthalmic primary delusional parasitosis includes real parasitosis, psychiatric illness, substance use, and organic ophthalmic or medical pathology. Patients may present with ocular symptoms other than their parasitic delusion such as vision loss or eye pain. Therefore, a full work up is necessary 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, or withdrawal from any of these.

Associated Conditions

Patients with DP often have other coexisting psychiatric conditions, making primary DP a diagnosis of exclusion. 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 or work up secondary psychiatric causes for patients with ophthalmic DP. Common psychiatric comorbidities of DP include depression, anxiety, schizophrenia, and obsessive-compulsive disorder, all of which may exacerbate the delusion. Thus, acceptance and willingness to seek treatment may be complicated by the underlying psychiatric condition.

Management

General treatment

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 pruritus, pain, or other complaints. For more severe cases of DP, often atypical antipsychotics such as risperidone, olanzapine, and quetiapine are used for psychopharmacological management. However, patients often refuse antipsychotic therapy. Medication adherence is more likely when patients are counseled that they are not being prescribed antipsychotics for schizophrenia. Rather, psychiatrists and dermatologists frequently use them to treat distress related to the parasitosis, and the antihistamine activity of antipsychotics can help to reduce itching.

Medical follow up

Consistent multidisciplinary follow up bolster the patient physician relationship and is advised for successful patient treatment.

Complications

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. Cases of ocular DP, regardless of etiology, can therefore result in disastrous ophthalmic outcomes due to complications related to scratching, picking, and excoriation of the eyelids, ocular adnexa, and cornea.

Prognosis

Patients with DP typically do not usually suffer marked impairment directly due to the DP. However, the delusions and associated symptoms such as pruritus 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. Serial follow up with a strong provider-patient relationship as well as management of any psychiatric comorbidity is also critical in achieving a satisfactory outcome in DP.