**Question:** Lalu Prasad, a 45-year-old male, presents to the OPD with a complaint of a continuous, non-progressive headache for the past 7 days. He believes that he has a brain tumor as he has consulted many neurologists in the past, and all investigations have been within normal limits. Pt requested for other investigation to reveal that he has brain tumor. Psychiatric evaluation shows the disease on the background of normal investigation. The most probable diagnosis is?

A. Hypochondriasis
B. Psychogenic headache
C. Functional neurological symptom disorder
D. Migraine

**Core Concept:** Psychogenic disorders are psychological conditions that can present with physical symptoms due to dissociation between the patient's conscious perception of their symptoms and the underlying physiological mechanisms. In this case, we are discussing a patient with normal investigations who presents with a clinical picture of a brain tumor but is actually suffering from a psychiatric disorder.

**Why the Correct Answer is Right:**

C. Functional neurological symptom disorder (FNSD) is the most appropriate diagnosis in this scenario. FNSD is characterized by the presence of neurological symptoms that are not explained by a structural brain disorder. In this case, the patient has symptoms consistent with a brain tumor, but normal investigations rule out a structural cause. Psychiatric evaluation reveals dissociation between the patient's conscious perception of symptoms and the underlying physiological mechanisms, which is a hallmark of FNSD.

**Why Each Wrong Option is Incorrect:**

A. Hypochondriasis (Hypochondriac disorder) is a psychiatric condition characterized by an exaggerated fear of having a serious illness despite no objective evidence. In this case, the patient does not fear having an illness but rather has symptoms consistent with a brain tumor.

B. Psychogenic headache is a psychiatric condition characterized by headache resulting from psychological factors. However, in this case, the patient presents with neurological symptoms (brain tumor) rather than a headache.

D. Migraine is a type of primary headache disorder, not a condition related to neurological symptoms like brain tumor.

**Clinical Pearl:** Psychiatric disorders can present with physical symptoms, and differential diagnosis in such cases involves considering the presence of dissociation between the patient's conscious perception and the underlying physiological mechanisms. In this case, the patient's symptoms are consistent with a brain tumor, but the psychiatric evaluation reveals that the patient is aware of the lack of a physical cause for his symptoms. This dissociation between the patient's perception of symptoms and their underlying physiological mechanisms is a hallmark of functional neurological disorders like FNSD.