Differential Diagnosis

• Single most likely diagnosis
  • Delusional Disorder: This diagnosis is the most likely because the patient has a fixed, false belief (delusion) that a famous actor is in love with her, which is a classic example of a delusion of erotomanic type. The fact that she is able to maintain her job and does not exhibit hallucinations or disorganized speech further supports this diagnosis.
• Other Likely diagnoses
  • Schizophrenia: Although the patient does not exhibit hallucinations or disorganized speech, schizophrenia can sometimes present with only delusions. However, the lack of other symptoms and the fact that she is able to function normally in her job make this diagnosis less likely.
  • Brief Psychotic Disorder: This diagnosis could be considered if the patient's delusion were to resolve on its own within a month. However, the fact that she has been writing daily letters and trying to visit the actor's home suggests a more chronic condition.
• Do Not Miss
  • Neurosyphilis: This condition can cause delusions and should be considered in any patient with a new-onset psychotic symptom, especially if there is a history of sexually transmitted infections. Although it is unlikely, missing this diagnosis could have serious consequences.
  • Temporal Lobe Epilepsy: This condition can cause delusions and should be considered in any patient with a new-onset psychotic symptom, especially if there is a history of seizures or other neurological symptoms.
• Rare diagnoses
  • Capgras Syndrome: This is a rare condition in which a person believes that a friend or family member has been replaced by an imposter. Although it is not directly applicable to this case, it is a rare delusional disorder that could be considered if the patient's symptoms were to change.
  • Fregoli Syndrome: This is a rare condition in which a person believes that multiple people are actually the same person in disguise. Although it is not directly applicable to this case, it is a rare delusional disorder that could be considered if the patient's symptoms were to change.