Differential Diagnosis
The patient's CBC results and medical history suggest several possible diagnoses. Here's a categorized differential diagnosis:
Single most likely diagnosis
- Anisocytosis due to prednisone therapy: Long-term prednisone use can cause changes in red blood cell production, leading to anisocytosis (variation in red blood cell size), which may result in a high MCV (mean corpuscular volume) and normal hemoglobin and hematocrit levels. The patient's normal iron, ferritin, and C-reactive protein levels also support this diagnosis.
Other Likely diagnoses
- Chronic disease anemia with a normocytic component: Although the patient's hemoglobin and hematocrit are normal, the presence of myositis (an autoimmune disease) and long-term prednisone use may contribute to a chronic disease anemia with a normocytic component, which could be masked by the high MCV.
- Red blood cell membrane disorders: Conditions like hereditary spherocytosis or hereditary elliptocytosis can cause an increase in MCV and MCHC (mean corpuscular hemoglobin concentration). However, these disorders are less likely given the patient's age and lack of reported family history.
- Vitamin B12 or folate deficiency: Although the patient's iron and ferritin levels are normal, a deficiency in vitamin B12 or folate could cause an increase in MCV. However, this would typically be accompanied by other symptoms like neurological deficits or gastrointestinal issues.
Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Hemolytic anemia: Although the patient's lactate dehydrogenase (LDH) and indirect bilirubin levels are not provided, a hemolytic anemia (e.g., autoimmune hemolytic anemia) could be a life-threatening condition that requires prompt diagnosis and treatment.
- Bone marrow failure: A bone marrow failure syndrome (e.g., aplastic anemia) could cause a decrease in red blood cell production, leading to anemia. Although this is less likely given the patient's normal hemoglobin and hematocrit, it is essential to consider this possibility.
Rare diagnoses
- Paroxysmal nocturnal hemoglobinuria (PNH): A rare, acquired, life-threatening disease of the blood characterized by the destruction of red blood cells, bone marrow failure, and the potential for blood clot formation.
- Myelodysplastic syndrome (MDS): A group of disorders caused by poorly formed or dysfunctional blood cells, which can lead to anemia, infection, and bleeding. Although MDS is rare, it is essential to consider this possibility in patients with unexplained cytopenias and a history of autoimmune disease.