TO THE EDITOR
We were delighted to read the high-quality article by Xu et al[1] in the World Journal of Psychiatry in 2024. A 71-year-old man complained of feeling insects crawling on and biting his limbs. The patient looked for the insects while scratching the perceived affected areas on the limbs for 2 weeks, resulting in broken skin. However, he failed to find any insects and responded poorly to topical and antiallergic drugs prescribed by several dermatology departments. The patient developed a disturbed, unhappy, and sad mood and was referred to the psychiatry outpatient department. Visual and haptic hallucinations were suggested by the authors.
People experiencing haptic hallucinations often describe feeling sensations on their skin like insects and hallucinations, although these experiences are not detectable by others. These hallucinations are also called tactile hallucinations and are classified as a hallucination of bodily sensation. Although these hallucinations are a psychiatric issue, they are typically diagnosed by dermatologists because patients usually seek help for skin-related complaints[2]. The literature indicates that haptic hallucinations can be perceived as either touch or pain, and they may involve both hallucinatory and delusional elements. The sensation of insects crawling on the skin is referred to as “formication” and may be linked to a delusion of infestation. For the case discussed in this article, it is important to determine whether the thoughts are delusional and how long they last. If delusions are present, the diagnosis needs to be differentiated from somatic type delusional disorder. This condition is also known as Ekbom syndrome, which manifests as visual hallucinations and delusion of infestation (delusional parasitosis). Delusional parasitosis is characterized by a strong, persistent belief in having a parasitic infection despite clear evidence to the contrary[3,4]. Delusional parasitosis involves the sensation of insect infestation on or in the skin or an internal parasite. Haptic hallucinations can occur in various psychiatric disorders, such as schizophrenia, delusional disorder, bipolar disorder[5], major depressive disorder[3], and obsessive-compulsive disorder[6]. Delusional parasitosis that arises from medical conditions may be associated with several factors, including deficiencies in vitamin B12 and folate, diabetes neuropathy, hyperthyroidism[7], multiple sclerosis, encephalitis, meningitis, tuberculosis, leprosy, syphilis, and human immunodeficiency virus[8]. Substance abuse, such as amphetamine, methamphetamine or cocaine use[3], can contribute to this syndrome. Alcohol withdrawal is another possible cause[7]. Additionally, side effects from medications such as ketoconazole, topiramate, amantadine, ciprofloxacin, phenelzine, and steroids have been linked to its development[9,10].
Patients diagnosed with dementia may exhibit visual and tactile hallucinations, as noted by Xu et al[1]. The authors specifically addressed the diagnosis of early Alzheimer’s disease (AD); however, they did not elaborate on the clinical progression or the hallmark symptoms typically associated with dementia in this patient, such as memory complaints, cognitive decline, difficulties with instrumental and basic activities of daily living, and impairments in executive functioning. It is essential to include the results of cognitive function assessments in these cases. Furthermore, the case history indicated that the patient experienced gait abnormalities, necessitating a thorough neurological examination, particularly an assessment of limb function and gait. Importantly, parkinsonism may manifest in patients with dementia with Lewy bodies (DLB), which is also associated with vivid visual hallucinations. DLB is recognized as the second most prevalent form of progressive neurodegenerative dementia following AD and is characterized by fluctuating cognitive functions, recurrent visual hallucinations, parkinsonism, and rapid eye movement sleep behavior disorder[11]. Visual hallucinations are considered one of the core neuropsychiatric symptoms in DLB and are one of the diagnostic criteria for this condition. Additionally, delusional parasitosis may occur in patients with DLB[12].
The authors could improve their discussion by providing further details regarding the patient’s affective symptoms, particularly depression. Symptoms of depression may encompass diminished interest, alterations in weight or appetite, sleep disturbances, fatigue, feelings of worthlessness or guilt, negative thought patterns, and even suicidal ideation. Depression is frequently observed as a prodromal symptom of dementia and is a commonly recognized behavioral and psychological symptom associated with this condition[13].
The prevalence of psychosis among older adults has not been systematically studied. Reports indicate a prevalence rate of 1.7% for psychosis in this demographic, with a lifetime incidence of 4.7%[14]. However, these figures do not include individuals residing in nursing homes or hospitals, where patients with dementia and delirium often present with psychosis. Psychotic symptoms may represent the clinical manifestation of disorders that originate earlier in life, such as schizophrenia; however, for a significant number of older adults, these symptoms may emerge for the first time in later life. Psychotic symptoms in elderly individuals most commonly occur in people with dementia. Conversely, the emergence of psychotic symptoms in older individuals does not necessarily indicate dementia; other conditions, including mood disorders, schizophrenia spectrum disorders, delirium, endocrinological disorders, substance use disorders, and various neuropsychiatric conditions (such as stroke, multiple sclerosis, limbic encephalitis, epilepsy, normal pressure hydrocephalus, prion diseases, motor neuron disease, Huntington’s disease, neoplasms, and autoimmune diseases), may also contribute to these symptoms[15].
From a pathophysiological perspective, the striato-thalamic-parietal circuitry may be involved in delusional infestation and visual hallucinations. Subcortical vascular encephalopathy, ischemic brain lesions, and putamen and striatum lesions are reportedly associated with delusional infestation[16]. The patient described by Xu et al[1] had hypertension and hyperlipidemia, which are chronic diseases. Although magnetic resonance imaging of the brain was not reported, computed tomography examination revealed several lacunar infarctions over the basal ganglion, which suggests the possibility of small vessel disease in other areas of the brain. This finding may also indicate hypoperfusion and ischemic lesions that involve a brain area that mediates visuotactile perception. Moreover, the aging process decreases the levels of estrogen and disturbs its neuroprotective role. A decrease in estrogen levels during the aging process alters striatal dopamine transporter (DAT) functions. The DAT is a presynaptic plasma membrane protein that is responsible for maintaining an appropriate level of dopamine in the intersynaptic space[17]. DAT dysfunction leads to increased extracellular striatal dopamine levels in the synapses, which is linked to disturbances in perception and thinking (tactile hallucinations and delusions). In addition to the dopamine hypothesis for psychotic symptoms, another rationale for the use of antipsychotics in managing visual and tactile hallucinations is related to the associated scratching behavior. Increased dopamine levels at the synapses secondary to DAT dysfunction appear to be associated with itching sensations in patients due to the activation of dopaminergic neurons in the ventral tegmental area and projections to the nucleus accumbens. Scratching behaviors induced by itching reportedly stimulate these dopaminergic neurons, which are also associated with increased dopamine release in the nucleus accumbens[18,19].
For patients diagnosed with early AD, the administration of acetylcholinesterase inhibitors (AChEIs) may be indicated. AChEIs offer a notable advantage over antipsychotic medications in the management of psychiatric symptoms associated with dementia, because AChEIs do not impair cognitive function and are associated with a reduced incidence of extrapyramidal side effects[20]. Consequently, clinicians may consider utilizing AChEIs as a primary intervention for the treatment of dementia and its accompanying psychotic symptoms, in addition to the potential combination of AChEIs with antipsychotics to treat neuropsychiatric manifestations[21,22]. If AChEIs prove to be inefficient, the introduction of antipsychotic medications may be warranted as a subsequent treatment option.
