Differential Diagnosis

• Single most likely diagnosis
  • Delusional disorder: The patient's belief that his neighbors are using toxic fumes to kill him is a delusion, which is a key feature of delusional disorder. The patient's symptoms, such as anxiety, worry, and decreased appetite, are also consistent with this diagnosis. The lack of hallucinations, disorganized thinking, and other psychotic symptoms makes delusional disorder a more likely diagnosis than other psychotic disorders.
• Other Likely diagnoses
  • Anxiety disorder: The patient's symptoms of anxiety, worry, and difficulty sleeping are consistent with an anxiety disorder, such as generalized anxiety disorder.
  • Depressive disorder: The patient's symptoms of decreased appetite, fatigue, and difficulty concentrating are also consistent with a depressive disorder, such as major depressive disorder.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Toxic exposure: Although the patient's belief about toxic fumes is likely a delusion, it is still important to rule out the possibility of actual toxic exposure, which could be a medical emergency.
  • Brain tumor or other neurological disorder: Although the CT scan of the head was normal, it is still important to consider the possibility of a brain tumor or other neurological disorder that could be causing the patient's symptoms.
• Rare diagnoses
  • Paranoid schizophrenia: Although the patient's symptoms are not typical of schizophrenia, it is still possible that he could have a rare form of the disorder, such as paranoid schizophrenia.
  • Factitious disorder: The patient's symptoms could also be fabricated or exaggerated, which would be consistent with a factitious disorder. However, this diagnosis would require further evaluation and evidence of fabrication or exaggeration.