Delusional Infestation and Chronic Pruritus: A Review. 
The literature on chronic pruritus, paresthesia and delusional infestation indicates that a wide variety of conditions ranging from AIDS to vitamin deficiencies may cause these symptoms.  In many, or perhaps most of these cases, activation of itch pathways seems to be the underlying cause of the skin sensations and perhaps even the visual hallucinations characteristic of delusional infestation.  The principle difference between diagnoses of chronic pruritus and delusional infestation appears to lie in the patient's interpretation of the cause of the symptoms, rather than underlying physiological differences.  Delusional infestation, paresthesia and chronic pruritus must be considered symptoms of underlying conditions.