Differential Diagnosis for Anxiety, Sad Mood, and Lack of Interest

Single Most Likely Diagnosis

• Major Depressive Disorder (MDD): This is the most likely diagnosis given the combination of symptoms such as sad mood, lack of interest, and anxiety, which are common presentations of MDD. The presence of these symptoms together often points towards a depressive disorder.

Other Likely Diagnoses

• Anxiety Disorder: While anxiety can be a symptom of MDD, it can also be a standalone diagnosis. Conditions like generalized anxiety disorder (GAD), panic disorder, or social anxiety disorder could present with significant anxiety and potentially some depressive symptoms.
• Adjustment Disorder with Mixed Anxiety and Depressed Mood: This diagnosis is considered when the symptoms are triggered by a specific stressor and do not meet the full criteria for MDD or an anxiety disorder.
• Bipolar Disorder: Although less likely without a clear history of manic or hypomanic episodes, bipolar disorder can present with depressive episodes that include anxiety and lack of interest.

Do Not Miss Diagnoses

• Thyroid Disorders (Hypothyroidism or Hyperthyroidism): Both can cause mood changes, including depression and anxiety. Missing these diagnoses could lead to inappropriate treatment and worsening of symptoms.
• Adrenal Insufficiency (Addison's Disease): This rare condition can cause depression, anxiety, and fatigue among other symptoms. It's critical to diagnose and treat promptly to prevent life-threatening complications.
• Neurodegenerative Diseases (e.g., Early Stages of Dementia, Parkinson's Disease): These conditions can present with mood changes, including depression and anxiety, and are crucial to identify for appropriate management.

Rare Diagnoses

• Wilson's Disease: A genetic disorder that leads to copper accumulation in the body, potentially causing psychiatric symptoms including depression and anxiety.
• Vitamin Deficiencies (e.g., Vitamin B12 Deficiency): Can cause neurological and psychiatric symptoms, including depression and anxiety.
• Chronic Fatigue Syndrome: Characterized by persistent fatigue that is not relieved by rest, it can also include symptoms of depression and anxiety.

Each of these diagnoses requires careful consideration of the patient's full clinical picture, including history, physical examination, and laboratory tests, to ensure accurate diagnosis and appropriate treatment.