What disorders are associated with delusional parasitosis?

Disorders Associated with Delusional Parasitosis

Delusional parasitosis is commonly associated with frontotemporal dementia (particularly C9orf72 mutation carriers), primary psychiatric disorders, neurological conditions, and certain medical conditions that affect brain function. 1, 2

Neurological Disorders

Frontotemporal Dementia (FTD)

• C9orf72 mutation carriers frequently present with somatic delusions, including parasitosis 1
  • Delusions occur in 21-56% of these patients
  • May precede classical FTD symptoms by up to a decade
  • Often accompanied by other psychiatric symptoms

Other Neurological Conditions

• Cerebrovascular disease 3
• Brain cysticercosis 3
• Encephalitis lethargica with basal ganglia lesions 1
• Sydenham chorea 1
• Neuroacanthocytosis 1
• Frontal lobe lesions 1
• Vitamin B12 deficiency-related dementia 3

Primary Psychiatric Disorders

Psychotic Disorders

• Schizophrenia 1
• Schizoaffective disorder 1
• Delusional disorder, somatic type (primary delusional parasitosis) 2
• Bipolar disorder with psychotic features 1
• Depression with psychotic features 1

Other Psychiatric Conditions

• Obsessive-compulsive disorder (OCD) - when focused on contamination concerns 4
• Personality disorders with somatic preoccupations 4

Medical Conditions

Substance-Related

• Drug intoxication or withdrawal 1, 2
• Medication side effects (particularly stimulants) 1

Systemic Conditions

• Endocrine disorders 1
• Autoimmune diseases 1
• Neoplasms and paraneoplastic processes 1
• Infections 1
• Genetic or metabolic disorders 1
• Nutritional deficiencies 1
• Peripheral neuropathy (contributing to pruritus and paresthesia) 3

Risk Factors and Clinical Patterns

Demographic Factors

• More common in females 5
• Typically affects individuals over 50 years of age 5, 3
• Can spread within family units through psychological contagion 5

Clinical Features

• Fixed, false belief of infestation despite medical evidence to the contrary 2
• "Matchbox sign" or "Digital pics sign" - bringing supposed evidence of parasites 5
• Often accompanied by:
  • Depression 3
  • Cognitive decline 3
  • Pruritus or paresthesia 3
  • Olfactory hallucinations 5
  • Self-harm behaviors to remove "parasites" 5

Diagnostic Approach

Key Considerations

• Distinguish between primary delusional parasitosis and secondary forms 2
• Rule out actual infestations and other medical causes 6
• Assess for cognitive impairment, especially in elderly patients 3
• Screen for genetic mutations (especially C9orf72) in patients with family history of FTD, ALS, or late-onset psychiatric disorders 1

Red Flags for Neurological Causes

• New onset in elderly patients 3
• Cognitive decline 3
• Neurological symptoms (paresthesia, motor symptoms) 3
• Family history of neurodegenerative disease 1

Management Implications

• Antipsychotics are the treatment of choice for primary delusional parasitosis 2, 7, 6
• For secondary forms, treat the underlying condition 2
• Multidisciplinary approach involving dermatology, psychiatry, and neurology 7
• C9orf72 genetic testing should be considered in cases with family history of FTD, ALS, or late-onset psychiatric disorders 1

The most challenging aspect of management is engaging patients in psychiatric treatment, as they typically reject the psychiatric nature of their symptoms and may lose faith in professional medicine 2.