Differential Diagnosis for a 65-year-old Woman with Fatigue, Nausea, Pallor, and Glossitis

• Single Most Likely Diagnosis
  • Vitamin B12 deficiency: The patient's vegan diet and low vitamin B12 level are strong indicators of this diagnosis. Vitamin B12 deficiency can cause fatigue, nausea, pallor, and glossitis, making it the most likely diagnosis given the patient's symptoms and lab results.
• Other Likely Diagnoses
  • Iron deficiency anemia: Although the serum ferritin level is 50, which is within the normal range, the patient's symptoms of fatigue, pallor, and glossitis could still suggest iron deficiency anemia, especially if the ferritin level is at the lower end of the normal range. However, the presence of a normal ferritin level makes this less likely than vitamin B12 deficiency.
  • Hypertension-related side effects: The patient's long-term use of lisinopril for hypertension management could potentially contribute to her symptoms, such as fatigue and nausea, although this is less directly related to the specific findings of pallor and glossitis.
• Do Not Miss Diagnoses
  • Gastric cancer: Although rare, gastric cancer can cause vitamin B12 deficiency due to impaired absorption. Given the patient's age and symptoms, it is crucial to rule out this potentially life-threatening condition.
  • Celiac disease: This autoimmune disorder can lead to malabsorption of vitamin B12 and iron, causing similar symptoms. It is essential to consider celiac disease to avoid missing a treatable condition that could have significant long-term consequences.
  • Pernicious anemia: An autoimmune condition leading to vitamin B12 deficiency, pernicious anemia is a critical diagnosis not to miss, as it requires specific treatment and can have severe consequences if left untreated.
• Rare Diagnoses
  • Other malabsorptive disorders (e.g., Crohn's disease, ulcerative colitis): These conditions can also lead to vitamin B12 and iron deficiencies but are less likely given the patient's presentation and lack of other symptoms suggestive of these diseases.
  • Intrinsic factor deficiency: A rare condition where the body is unable to produce intrinsic factor, necessary for vitamin B12 absorption, could be considered but is much less common than pernicious anemia or dietary deficiencies.