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Massive plasmocytosis due to methimazole-induced bone marrow toxicity

D V Breier1, P Rendo, J Gonzalez

  • 1Division of Hematology, Hospital General de Agudos "Carlos G. Durand", Buenos Aires, Argentina. dbreier@intramed.net.ar

American Journal of Hematology
|July 10, 2001
PubMed

Insights

Methimazole (MMI) therapy for Graves' disease can cause pancytopenia, a rare condition. This case highlights MMI-induced pancytopenia presenting as massive bone marrow plasmocytosis, not aplastic anemia.

Area of Science:

  • Endocrinology
  • Hematology
  • Pharmacology

Background:

  • Thionamide therapy, including methimazole (MMI), is a standard treatment for Graves' disease.
  • Pancytopenia is a rare but serious adverse effect of thionamide therapy, typically associated with aplastic anemia and hypocellular bone marrow.
  • Massive bone marrow plasmocytosis is characteristic of multiple myeloma, not typically seen with drug-induced pancytopenia.

Observation:

  • A 16-year-old female with Graves' disease on methimazole developed pancytopenia and sepsis.
  • Bone marrow examination revealed massive plasmocytosis (98% plasma cells) mimicking multiple myeloma, a presentation distinct from the usual hypocellular marrow in thionamide-induced aplastic anemia.
  • Discontinuation of methimazole and supportive care led to rapid hematological recovery, with plasma cells decreasing to 6% within 4 days and normalization of blood counts.

Findings:

  • This case represents the first reported instance of methimazole-induced pancytopenia presenting with profound bone marrow plasmocytosis.
  • The patient's presentation mimicked multiple myeloma, highlighting the importance of considering drug toxicity in the differential diagnosis of pancytopenia with plasmacytic hyperplasia.
  • Hematological parameters and bone marrow morphology normalized after methimazole withdrawal, confirming drug-induced etiology.

Implications:

  • Clinicians should consider methimazole-induced pancytopenia with plasmocytosis in patients with Graves' disease presenting with cytopenias.
  • This finding expands the known spectrum of hematological adverse effects associated with thionamide therapy.
  • Early recognition and discontinuation of the offending agent are crucial for favorable outcomes in drug-induced bone marrow toxicity.

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