DOI: 10.1056/NEJMicm066861
Keywords: marrow hyperplasia, β-thalassemia, bone marrow expansion, radiographic features, differential diagnosis, hematology, skeletal changes, chronic anemia
Abstract
Marrow hyperplasia, also known as bone marrow expansion or medullary hyperplasia, represents a compensatory physiological response to chronic anemia or hematologic stress. It is a hallmark of several inherited and acquired disorders, including β-thalassemia. This article provides a comprehensive discussion of marrow hyperplasia from pathophysiological mechanisms to radiological interpretation, diagnostic differentials, and management, illustrated through a clinical case of a 39-year-old woman with β-thalassemia major. This discussion integrates the latest literature and aims to serve as a concise yet authoritative review for clinicians, radiologists, and medical examinees.
1. Case Summary
A 39-year-old woman with β-thalassemia major has required monthly red blood cell transfusions since the age of one. She began iron chelation therapy at age six due to transfusion-related iron overload. Presenting symptoms included bilateral ankle pain, swelling, and restricted joint mobility.
Laboratory evaluation revealed:
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Hemoglobin: 8.3 g/dL
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Mean corpuscular volume (MCV): 81.3 µm³
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Red cell distribution width (RDW): 26.7%
Family history was significant for a brother who also suffered from β-thalassemia and died of heart failure at age 31.
Figure 1. Normal Tibial Radiograph
Baseline anterior–posterior (AP) radiograph of the tibia showing normal cortical and trabecular bone architecture without evidence of medullary expansion or cortical thinning.
Figure 2. Tibia with “Spider-Web” Trabecular Pattern
AP radiograph of the tibia demonstrating a reticulated, “spider-web” trabecular pattern typical of marrow hyperplasia due to chronic erythroid expansion in β-thalassemia.
Figure 3. Skull
hair-on-end appearance (classic): unusual in patients after the age of nine in treated patients, widening of the diploic space, thinning of the inner and outer table, the occipital bone is spared, due to a lack of hemopoietic bone marrow.
2. Pathophysiology of Marrow Hyperplasia
Marrow hyperplasia refers to the expansion of hematopoietically active marrow within the medullary cavity, driven by increased demand for erythropoiesis. In β-thalassemia, defective β-globin synthesis leads to ineffective erythropoiesis, severe anemia, and compensatory marrow expansion.
Key mechanisms include:
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Increased Erythropoietin (EPO) secretion → stimulates erythroid precursors.
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Medullary cavity expansion → bone remodeling and cortical thinning.
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Extramedullary hematopoiesis (EMH) → when marrow expansion exceeds bone capacity, leading to hematopoietic tissue formation in liver, spleen, or paraspinal regions.
Histologically, hypercellular marrow shows erythroid hyperplasia with reduced fat content. Chronic expansion results in skeletal deformities such as frontal bossing, maxillary hypertrophy, and osteopenia.
3. Epidemiology
Marrow hyperplasia is not a standalone disease but a secondary manifestation of hematologic disorders. It is most prevalent in:
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β-thalassemia major and intermedia
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Sickle cell anemia
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Chronic hemolytic anemias
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Myeloproliferative disorders
Globally, β-thalassemia affects approximately 1.5% of the population, with high prevalence in Mediterranean, Middle Eastern, South Asian, and Southeast Asian populations. Improved transfusion regimens and chelation therapy have increased survival, but skeletal manifestations remain common in under-transfused patients.
4. Clinical Presentation
Symptoms arise from both anemia-related and skeletal consequences of marrow expansion:
| System | Typical Manifestations |
|---|---|
| Hematologic | Fatigue, pallor, weakness, exertional dyspnea |
| Skeletal | Bone pain (especially long bones and face), deformities, pathologic fractures |
| Craniofacial | “Chipmunk facies,” frontal bossing, malocclusion |
| Musculoskeletal | Reduced bone density, arthralgia, restricted mobility |
| Systemic | Hepatosplenomegaly due to extramedullary hematopoiesis |
In the present case, ankle pain and swelling were manifestations of localized marrow expansion and secondary cortical stress.
5. Imaging Features
Radiological examination plays a critical role in diagnosing marrow hyperplasia.
X-ray Findings:
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Widened medullary cavity
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Thinning of cortical bone
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Coarsened or “spider-web” trabecular pattern
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Hair-on-end appearance in skull radiographs (due to perpendicular trabeculae)
MRI Findings:
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Low T1 and high T2 marrow signal (reflecting high cellularity and low fat)
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Diffuse red marrow reconversion
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Heterogeneous enhancement after gadolinium administration
CT Findings:
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Cortical thinning, trabecular coarsening, and expansion of diploic space
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Useful for differentiating from osteomalacia or malignancy
Figure Interpretation:
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Figure 1: Normal tibia with preserved cortical margin and homogenous trabeculae.
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Figure 2: Distinct “spider-web” trabecular pattern, consistent with marrow hyperplasia secondary to β-thalassemia.
6. Differential Diagnosis
| Condition | Distinguishing Features |
|---|---|
| Ewing’s sarcoma | Destructive lesion with periosteal reaction; localized pain |
| Osteomalacia | Generalized demineralization, Looser zones |
| Polyostotic fibrous dysplasia | Ground-glass matrix, cortical thinning, deformity |
| Osteopetrosis | Diffuse sclerosis, obliterated medullary cavity |
| Marrow hyperplasia | Symmetric medullary expansion, coarse trabeculae, associated with anemia |
In this patient, the symmetrical involvement, hematologic history, and absence of destructive cortical lesions favored marrow hyperplasia.
7. Diagnosis
Diagnosis integrates clinical, hematologic, and imaging findings:
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Chronic anemia with high reticulocyte count
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Radiographic marrow expansion
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Exclusion of malignancy or infection
MRI is the gold standard for marrow assessment, while biopsy confirms cellular hyperplasia without dysplasia or neoplasia.
8. Treatment and Management
1. Treat Underlying Cause
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Regular transfusion therapy to suppress ineffective erythropoiesis.
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Maintain pre-transfusion Hb > 9.5 g/dL to prevent marrow expansion.
2. Iron Chelation
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Prevent secondary hemochromatosis due to transfusion overload.
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Common agents: Deferoxamine, Deferiprone, Deferasirox.
3. Bone Health Management
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Calcium, Vitamin D, Bisphosphonates to preserve bone density.
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Orthopedic management for fractures or deformities.
4. Curative Therapy
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Allogeneic bone marrow transplantation (BMT) or gene therapy offers potential cure.
9. Prognosis
Prognosis depends on anemia control and iron toxicity prevention.
Well-managed β-thalassemia patients can survive into middle age with minimized skeletal deformities.
Untreated or under-transfused cases show progressive bone deformity, extramedullary hematopoiesis, and organ failure secondary to iron overload.
Quiz
Question 1. Which of the following best explains the radiographic “spider-web” trabecular pattern in marrow hyperplasia?
A. Cortical bone destruction by malignant cells
B. Expansion of hematopoietic marrow and trabecular remodeling
C. Deposition of iron within trabeculae
D. Vascular necrosis of bone marrow
✅ Answer: B
Explanation: Chronic erythroid expansion leads to trabecular thinning and remodeling, giving rise to a reticulated “spider-web” appearance.
Question 2. In β-thalassemia major, marrow hyperplasia primarily occurs due to:
A. Increased bone resorption by osteoclasts
B. Ineffective erythropoiesis and compensatory EPO stimulation
C. Vitamin D deficiency
D. Myelofibrosis
✅ Answer: B
Explanation: Defective β-globin synthesis causes ineffective erythropoiesis, stimulating erythropoietin-driven marrow expansion.
Question 3. Which imaging modality is most sensitive for detecting early marrow hyperplasia?
A. X-ray
B. CT
C. MRI
D. Bone scintigraphy
✅ Answer: C
Explanation: MRI detects marrow composition changes (fat to cellular conversion) earlier than radiographic or CT changes.
11. Conclusion
Marrow hyperplasia in β-thalassemia exemplifies the intricate interplay between hematologic disorders and skeletal remodeling. Recognizing the imaging patterns and clinical correlations is vital for differential diagnosis and for preventing irreversible bone deformities. Early and adequate transfusion therapy remains the cornerstone for managing this compensatory yet pathologic process.
References
[1] Rund, D., & Rachmilewitz, E. “β-Thalassemia,” New England Journal of Medicine, vol. 353, no. 11, pp. 1135–1146, 2005.
[2] Weatherall, D.J., “The Thalassemias: Disorders of Globin Synthesis,” Hematology: Basic Principles and Practice, 7th ed., 2023.
[3] Musallam, K.M. et al., “Bone disease in β-thalassemia: Pathophysiology and management,” Blood Reviews, vol. 33, pp. 14–29, 2019.
[4] Wood, J.C. “Use of MRI to monitor iron overload in thalassemia,” Annals of the New York Academy of Sciences, vol. 1202, pp. 36–44, 2010.
[5] Cappellini, M.D., Porter, J.B., et al., “Guidelines for the Management of Transfusion Dependent Thalassemia,” Thalassemia International Federation, 4th Edition, 2021.
[6] Papanikolaou, G., & Pantopoulos, K. “Iron metabolism and toxicity,” Toxicology and Applied Pharmacology, vol. 202, no. 2, pp. 199–211, 2005.
[7] Maccio, A., & Madeddu, C. “Bone marrow changes in chronic anemia,” Frontiers in Oncology, vol. 11, 2021.
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