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A patient with delusional parasitosis secondary to herpes zoster and comorbid depression: a case report

Delusional parasitosis (DP), a rare psychosis typified by the unshakeable and mistaken belief that an individual is infected with insects or parasites, is mainly considered a monosymptomatic hypochondriacal psychosis. It meets the Diagnostic and Statistical Manual of Mental Disorders, 5th edition, criteria for a delusional disorder. Until now, the literature, including case reports, case series, and systematic reviews, has indicated that antipsychotics that inhibit presynaptic dopamine reuptake at the dopamine transporter are the most effective to treat DP. Serotonergic medications have also been found to be effective. Here, we describe the diagnosis and management of an elderly female patient with refractory DP secondary to herpes zoster and comorbid depression. A 69-year-old woman first presented to us on 26 February 2018 and complained of a 3-year history of perceiving there to be small bugs crawling under her skin and biting her, which caused itching. She had no specific psychiatric history, organic disorders, cranial trauma history, medication history, substance exposure, or family history of psychiatric disorder. In 2015, she had visited a community hospital for abdominal herpes zoster but did not receive formal treatment so that she continued to experience itching. A few months after her visit, she was convinced that some bugs were crawling in her anterior abdomen and biting her. This prompted the patient to puncture her skin with a needle. Gradually, the crawling and biting sensations appeared in the patient’s anterior chest, limbs, face, and mouth. To cope, the patient scratched her skin and used insecticide to remove the bugs, although her close relatives were able to repeatedly persuade her that no bugs were crawling on her skin. However, she felt distressed, experienced loss of interest, and became unwilling to communicate with others. In February 2018, she presented at the dermatological department of our hospital with damage to her skin. Laboratory tests,including biochemical and thyroid function tests, prolactin, serum B12, folate level, HIV, syphilis, and hepatitis screening, homocysteine, and pemphigus antibody, electrocardiogram, and chest and abdominal CT were within normal limits. During her stay in the hospital, she also said that snakes slithered across her limbs and face and bit her. After ineffective glucocorticoid therapy and negative skin biopsy, parasitic infection and pemphigus disease were ruled out, and the patient was sent to a neuropsychologist. During the patient’s visit to the neuropsychological department, she denied having visuo-tactile hallucinations and, in the psychiatric examination, presented without apparent deficits in instant recall, visuospatial/executive functions, verbal fluency, or computing ability. The Mini-Mental State Examination and the Patient Health Questionnaire-9 were administered, and the patient scored a 24 and 10, respectively. (The patient did not complete primary school.) Physical examination was negative except for multiple skin lesions (Fig. 1). Brain magnetic resonance imaging showed multiple lacunar infarctions in the right basal ganglia and bilateral corona radiata, as well as bilateral hippocampal atrophy (Fig. S1). The patient underwent psychological counselling and was prescribed fluvoxamine maleate and olanzapine. The time axis of medications is shown in Table S1. Our patient was at an increased risk for visuotactile hallucinations secondary to herpes zoster without formal treatment, which may be related to autoimmune system dysregulation due to the viral infection and/or the insomnia, mental tension, and anxiety caused by itching. Thorough dermatological, psychiatric, and imaging examinations, pathological skin biopsy, and laboratory tests for the differential diagnosis, we ruled out psychiatric disorders, including dementia, schizophrenia, affective psychoses, substance use and medication-induced disorders, and identified no somatic disorders except for herpes zoster in the past. Given that the patient felt distressed and experienced loss of interest based on