Differential Diagnosis for 41-year-old Male with Fatigue, Headache, and Nausea

• Single Most Likely Diagnosis
  • Viral illness (e.g., influenza, common cold): The patient's symptoms of fatigue, headache, and nausea, along with his son experiencing similar symptoms, suggest a contagious viral illness. The mild nature of the symptoms and the absence of severe findings support this diagnosis.
• Other Likely Diagnoses
  • Sinusitis: The patient's complaint of a mild frontal bilateral headache could indicate sinusitis, especially if the headache is accompanied by facial pressure or nasal congestion.
  • Migraine: Although less likely given the bilateral nature of the headache, migraines can present with nausea and fatigue, and some patients may experience bilateral headaches.
  • Gastroenteritis: If the nausea were to progress to vomiting or if diarrhea were present (not mentioned but possible), gastroenteritis could be considered, especially in the context of similar symptoms in a household member.
• Do Not Miss Diagnoses
  • Meningitis: Although the patient's symptoms are mild and vitals are stable, meningitis can present with headache, nausea, and fatigue. The severity and potential for rapid progression make it crucial not to miss this diagnosis, despite its lower likelihood.
  • Encephalitis: Similar to meningitis, encephalitis is a serious condition that can present with non-specific symptoms such as headache and fatigue, especially in its early stages.
  • Subarachnoid Hemorrhage: A sudden, severe headache (often described as "the worst headache of my life") can be a sign of a subarachnoid hemorrhage. Although the patient's headache is described as mild, any headache with a sudden onset warrants consideration of this diagnosis.
• Rare Diagnoses
  • Chronic Fatigue Syndrome: If the patient's fatigue persists over time without a clear cause, chronic fatigue syndrome could be considered, though it's less likely given the acute presentation.
  • Neurodegenerative Diseases: Certain neurodegenerative diseases can present with non-specific symptoms such as fatigue and headache, but these would be extremely rare and unlikely without other significant findings.
  • Mitochondrial Diseases: These are a group of disorders caused by dysfunctional mitochondria and can present with a wide range of symptoms including fatigue, but they are rare and typically have other distinctive features.