Differential Diagnosis

The patient's presentation of paranoia, withdrawal, poor self-care, sleep disturbances, diminished appetite, auditory hallucinations, and delusions of poisoning suggests a psychiatric or neurological condition. The presence of a painless ulcer on the hard palate and a positive ANA screen adds complexity to the diagnosis. Here is a categorized differential diagnosis:

• Single most likely diagnosis
  • Schizophrenia: The patient's symptoms of paranoia, withdrawal, auditory hallucinations, and delusions are classic for schizophrenia, especially given the acute onset and the absence of other explanatory medical conditions.
• Other Likely diagnoses
  • Systemic Lupus Erythematosus (SLE): The positive ANA screen and the presence of a painless oral ulcer are suggestive of SLE, which can also cause psychiatric symptoms, including psychosis.
  • Depression with Psychotic Features: Although less likely given the prominent hallucinations and delusions, depression with psychotic features could explain some of the patient's symptoms, including sleep disturbance, diminished appetite, and poor self-care.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Neurosyphilis: Despite the normal CT scan, neurosyphilis can cause psychiatric symptoms, including psychosis, and is known to cause painless oral ulcers in its primary stage. The diagnosis would be critical due to its treatability.
  • Vitamin B12 Deficiency: This condition can cause neurological and psychiatric symptoms, including psychosis, and is important to rule out due to its reversibility with treatment.
• Rare diagnoses
  • Anti-NMDA Receptor Encephalitis: This is a rare autoimmune condition that can cause psychosis, hallucinations, and altered mental status, often with a fluctuating course. It's more commonly seen in young women and can be associated with a tumor.
  • Sjögren's Syndrome: Although less likely, this autoimmune disorder can cause psychiatric symptoms and is associated with a positive ANA. It often presents with dry eyes and mouth but can have systemic manifestations, including neurological and psychiatric symptoms.