How to manage a patient with psoriasis and macrocytic anemia (elevated Mean Corpuscular Volume (MCV) and Mean Corpuscular Hemoglobin (MCH))?

Management of Psoriasis with Macrocytic Anemia (Elevated MCV and MCH)

Patients with psoriasis who develop macrocytic anemia require thorough evaluation for vitamin B12 and/or folate deficiency, as these are the most common causes of megaloblastic anemia in psoriatic patients, particularly those who have received methotrexate therapy.

Diagnostic Approach

Initial Assessment

1. Evaluate medication history:

   • Check if patient is or was recently on methotrexate (can cause folate deficiency)
   • Review other psoriasis medications that may affect blood counts (e.g., hydroxyurea, azathioprine) 1

2. Laboratory workup:

   • Complete blood count with peripheral smear
   • Serum vitamin B12 levels
   • Serum folate and red cell folate levels
   • Liver function tests (elevated liver enzymes may contribute to macrocytosis)
   • Thyroid function tests (hypothyroidism can cause macrocytosis)
   • Reticulocyte count
   • Lactate dehydrogenase (LDH) and bilirubin (to assess for hemolysis)

Differential Diagnosis

Macrocytic anemia in psoriasis patients may be due to:

• Vitamin B12 deficiency (most common - 78.3% of megaloblastic anemia cases) 2
• Folate deficiency (particularly in methotrexate users) 3
• Combined B12 and folate deficiency (21.7% of megaloblastic anemia cases) 2
• Alcohol use (common cause of macrocytosis)
• Liver disease
• Myelodysplastic syndrome (consider in older patients not responding to vitamin replacement)
• Medication effect (methotrexate, hydroxyurea, azathioprine) 1

Management Algorithm

Step 1: Determine Cause of Macrocytic Anemia

• If vitamin B12 deficiency confirmed:

  • Administer vitamin B12 replacement (intramuscular or high-dose oral)
  • Investigate underlying cause (pernicious anemia, malabsorption, dietary deficiency)

• If folate deficiency confirmed:

  • Administer folate supplementation
  • If related to methotrexate therapy, consider adjusting dose or adding folate supplementation

• If combined deficiency:

  • Replace both vitamins (start B12 first to prevent neurological complications)

Step 2: Adjust Psoriasis Treatment

• If macrocytic anemia is medication-related:

  • Consider temporarily discontinuing or reducing dose of the offending agent
  • For methotrexate-induced folate deficiency, continue folate supplementation
  • Consider alternative psoriasis treatments with less hematologic toxicity

• For patients requiring systemic therapy:

  • Avoid medications with known bone marrow toxicity (e.g., hydroxyurea, azathioprine) 1
  • Consider biologics or other targeted therapies with less hematologic impact

Step 3: Monitoring

• Follow up complete blood count every 4-8 weeks until anemia resolves
• Monitor vitamin B12 and folate levels until normalized
• For unexplained macrocytosis without clear etiology, follow up with blood counts every 6 months 4
• Consider bone marrow biopsy if:
  • Anemia persists despite vitamin replacement
  • Other cytopenias develop
  • Patient is older (>55 years) with persistent unexplained macrocytosis 2

Special Considerations

Comorbidity Screening

Patients with psoriasis, especially moderate-to-severe disease, have increased risk for metabolic disorders including diabetes 1. Consider:

• Fasting blood glucose and/or HbA1c testing
• Lipid profile
• Blood pressure monitoring
• Weight/BMI assessment

Cautions and Pitfalls

1. Don't assume all macrocytosis in psoriasis patients is medication-related
2. Remember that 11.6% of patients with unexplained macrocytosis may develop primary bone marrow disorders 4
3. Avoid systemic corticosteroids for psoriasis management except in specific circumstances (erythrodermic psoriasis, generalized pustular psoriasis, or hyperacute psoriatic polyarthritis) 1
4. Be aware that some patients with megaloblastic features may have underlying myelodysplastic syndrome, especially if they don't respond to vitamin replacement 2

By systematically evaluating and managing both the macrocytic anemia and psoriasis, patients can achieve improved outcomes for both conditions while minimizing medication-related complications.