Abstract
Delusional parasitosis is a rare psycho-dermatological disorder that lacks standard management guidelines. We report a case of an elderly woman with long standing multiple dermatological illnesses who later developed delusional parasitosis. We highlight the pertinent diagnostic and therapeutic challenges. We support multidisciplinary collaborative care combining effective pharmacotherapy with efficient non-pharmacological measures.
Introduction
Delusional parasitosis, a psycho-dermatological disorder, presents with a patient's fixed belief that they are suffering from an infestation of living parasites, without corroborating medical evidence. 1 The low prevalence, the under diagnosis of the condition and the patients’ reluctance to seek psychiatric care 2 are reasons for the scarcity of published reports of clinical case series describing its characteristics and of randomized trials reporting efficacious treatment.
Antipsychotics are routinely employed in treatment but their use and duration have been debated because of the absence of standard management guidelines.
Recent systematic reviews focus only on primary delusional parasitosis and its pharmacological management. They overlook the inherent clinical complexity in differentiating between the primary and secondary forms of the disorder and do not mention the non-pharmacological treatment strategies. 3 We highlight these issues in our report of the case of an elderly woman who had suffered multiple established dermatological diagnoses for over three decades but who then developed delusional parasitosis, which remitted with multi disciplinary collaborative care.
Case history
Mrs S, a 70-year-old housewife, without a past or family history of any neuropsychiatric morbidity was referred to the Consultation Liaison Psychiatry clinic by the dermatology department of a tertiary care hospital. She described a three-month history of multiple insects crawling over her body and biting her. She had generalized itching and disturbed sleep. She displayed an empty matchbox containing the sample of ‘insects’. She had never abused any substances. On examination, dry eczematous skin lesions were present over her lower extremities. She had somatic delusions, tactile hallucinations and associated distress. She lacked insight and was averse to accept psychiatric care. The other components of her mental status and her systemic examinations were normal.
Complete blood counts, liver and thyroid function tests, creatinine, folic acid and vitamin B12 levels were within normal limits.
A review of her medical records revealed details of multiple and varied dermatological conditions and their treatments. Thirty years previously she had been diagnosed by skin biopsy as having borderline Hansen's disease, which was treated with dapsone monotherapy. Ten years later, she was treated for vitiligo and ichthyosis with recurrent episodes of asteatotic eczema. Over the next decade, she developed phytophotodermatitis with multiple exacerbations and secondary infection, which was managed with topical steroids and antibiotics. For her symptoms of persistent itching, she had been given a therapeutic trial of anti scabies treatment on more than one occasion. She had received inpatient care on eight occasions and had been meticulously followed up for three decades.
Although she recurrently manifested with generalized itching, she had only recently complained about the ‘insects’. Current dermatological evaluation, skin biopsy and mineral oil preparation were negative for any active lesions. A diagnosis of persistent delusional disorder (World Health Organization International Classification of Disease [ICD]-10: F 22.0) was made. Organic delusional disorder (ICD-10: F 06.2) was excluded, as she did not have a current central nervous or systemic pathology.
We neither corroborated nor confronted her belief. We acknowledged her distress and established a therapeutic relationship. She consented to psychiatric management only in order to cope with the ‘insects’, while she continued to consult dermatologists for her other complaints. We provided weekly sessions of supportive psychotherapy and risperidone, which was gradually increased to 4 mg/day. She stopped complaining about the infestation and began managing her household chores within four weeks. She regularly attended both outpatient clinics and maintained the improvement.
Discussion
Mrs S exemplifies the challenges in diagnosing and treating delusional parasitosis in patients with established dermatological illnesses.
The arbitrary categorization of primary and secondary forms is difficult and the clinical reality may represent a dimensional continuum. Hence, the benefits of proposing different management protocols and excluding the secondary forms in clinical trials are debatable; It is difficult, if not impossible, in many cases to establish whether the tactile hallucinations preceded the delusions of parasitosis or vice versa; It is often difficult to precisely date the onset of the condition because of the complex issues related to clinical presentation, the elicitation of symptoms, observer bias, inter-rater reliability and overlapping diagnostic boundaries; There is a lack of consensus on the efficacy and choice of the different psychotropic medications.
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The treatment strategy includes efforts to engage the patient in therapy, despite their reluctance for psychiatric care. The establishment of a therapeutic relationship and multidisciplinary care is useful and should precede the prescribing of antipsychotic medication. Monitoring medication compliance and ensuring regular follow up are mandatory for success. The good outcome in this case was as a result of effective pharmacotherapy combined with efficient non-pharmacological measures and is consistent with that reported by Srinivasan et al. 5