Psychiatric disorders due to a medical or neurological condition are the main differential diagnoses in newly admitted psychiatric patients, consultations and outpatient settings. Especially with the growing elderly population delirium occurs more frequently, often due to multiple causes. Although its prognosis is known to be unfavourable, delirium too often remains undiagnosed or untreated. Medications, neurological diseases, infections as well as metabolic and other medical conditions have to be ruled out in the differential diagnosis using the patient’s history, physical examination, laboratory results and imaging procedures. First-time psychiatric symptoms of an unknown medical disease as well as co-occurring psychiatric symptoms in chronic diseases provoke a challenging diagnostic decision, as reactive psychiatric symptoms have to be distinguished which is not always possible. In psychiatric disorders confirmed to be due to a medical condition, therapeutic implications are primarily geared to the causes of the disease. Only in a second step psychiatric medication is warranted with antipsychotic, antidepressant or sedation-inducing properties depending on the patient’s symptoms.
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