**Core Concept:**
The question is about a patient presenting with a psychiatric symptom, specifically the phenomenon of **Psychogenic Insectoid Dermatitis**, also known as **Delusional Infestation**. This is a delusional disorder where a patient believes they are infested with insects despite no evidence of actual infestation. It is often associated with psychiatric conditions like depression, anxiety, and schizophrenia.

**Why the Correct Answer is Right:**
In this case, the correct answer is **D. Delusional Infestation (Psychogenic Insectoid Dermatitis)**. This is the correct answer because the patient is experiencing a delusional disorder, believing that insects are crawling under his skin. This is not due to an actual infestation but is rather a manifestation of his psychological state, specifically his depression and psychosis induced by the cocaine binge.

**Why Each Wrong Option is Incorrect:**
A. **Phobic Parasitosis (Hysterical Infestation)** is similar to Delusional Infestation but is specific to patients who have a genuine fear of infestation, often due to a traumatic event. In this scenario, the patient has Delusional Infestation because he believes insects are present, not just fears them.

B. **Delusion of Parasitosis (Delusional Parasitosis)** is another similar disorder where patients fear being infested but does not involve a delusional component (believing insects are present).

C. **Delirium** is an acute confusion state due to organic causes like infection, drug withdrawal, or brain injury. In this case, the patient has a delusional disorder (Delusional Infestation) rather than delirium.

**Clinical Pearl:**
Delusional Infestation is a psychiatric disorder that should be distinguished from other dermatological conditions like eczema or insect bites, which may present with skin lesions. In such cases, a thorough psychiatric evaluation is necessary to address the patient's psychological concerns and manage their symptoms effectively.