Causes of Secondary Myelofibrosis
Secondary myelofibrosis develops from underlying conditions that trigger reactive bone marrow fibrosis, distinct from primary myelofibrosis which is a clonal myeloproliferative neoplasm.
Primary vs. Secondary Distinction
The WHO classification explicitly requires excluding secondary causes before diagnosing primary myelofibrosis 1. The key diagnostic criterion states that bone marrow fibrosis must not be secondary to infection, autoimmune disorder, chronic inflammatory condition, hairy cell leukemia, other lymphoid neoplasm, metastatic malignancy, or toxic (chronic) myelopathies 1, 2.
Major Categories of Secondary Myelofibrosis
Hematologic Malignancies
- Chronic myeloid leukemia (CML) - BCR-ABL1 positive disease
- Myelodysplastic syndromes (MDS)
- Other myeloproliferative neoplasms - particularly post-polycythemia vera and post-essential thrombocythemia myelofibrosis 3
- Multiple myeloma - can present with secondary myelofibrosis that significantly worsens prognosis 4
- Hairy cell leukemia and other lymphoid neoplasms 1
- Metastatic malignancy to bone marrow 1
Metabolic and Endocrine Disorders
- Primary hyperparathyroidism - a well-documented but rare cause where pancytopenia and myelofibrosis can reverse after parathyroidectomy 5
- Secondary hyperparathyroidism/renal osteodystrophy - particularly in hemodialysis patients, potentially reversible with parathyroidectomy 6
- Vitamin D deficiency - can cause myelofibrosis in early infancy with hepatic extramedullary hematopoiesis 7
Inflammatory and Autoimmune Conditions
Infectious Causes
Other Causes
- Toxic (chronic) myelopathies 1
- Reactive thrombocytosis conditions - including iron deficiency, splenectomy, surgery, infection, inflammation, and metastatic cancer 1
Clinical Pitfalls
A critical caveat: patients with conditions causing reactive myelofibrosis are not immune to developing primary myelofibrosis 1. If other diagnostic criteria for primary myelofibrosis are met (JAK2, CALR, or MPL mutations; characteristic megakaryocyte morphology; absence of BCR-ABL1), consider primary disease even when a potential secondary cause is present.
The pathophysiology involves platelet and megakaryocyte alpha-granule release of growth factors (like PDGF) that stimulate fibroblast proliferation 8. This explains why the fibrosis itself is reactive rather than neoplastic, even in primary myelofibrosis.
Diagnostic Approach
When evaluating myelofibrosis:
- First, test for driver mutations (JAK2, CALR, MPL) - their presence suggests primary disease 2
- Exclude BCR-ABL1 to rule out CML 1, 2
- Assess for dysplasia to exclude MDS 1
- Screen for metabolic causes - check calcium, PTH, and vitamin D levels, particularly in patients with renal disease or unexplained hypercalcemia 5, 6, 7
- Evaluate for systemic inflammatory or autoimmune conditions 1
- Consider imaging for metastatic disease if clinically indicated 1
The distinction matters because secondary myelofibrosis may be reversible if the underlying condition is treated effectively, as demonstrated with hyperparathyroidism 5, 6.