Question

An unmarried 29-year-old accountant is referred for a psychiatric evaluation by his corporate human resources department due to ongoing interpersonal difficulties. For the past seven years, he has worked in an isolated cubicle and consistently refuses to attend team meetings or company events. During the clinical interview, the patient sits rigidly, avoids eye contact, and appears visibly apprehensive. He explains that he avoids his colleagues because he is convinced they are harboring malicious intentions and secretly sabotaging his energy fields. He notes that this intense anxiety persists even with colleagues he has known for years. He describes his mind as being 'tuned to a specialized frequency that intercepts cosmic warnings.' His speech is markedly abstract and circumstantial, yet it remains goal-directed without derailment or neologisms. He firmly denies ever experiencing auditory or visual hallucinations. A review of his medical history reveals that these eccentric behaviors and beliefs have been present continuously since his late teens, without distinct episodes of clinical deterioration or full recovery. He denies any periods of pervasive sadness or elevated mood. Which of the following is the most likely diagnosis?