Multifocal Bone Infarcts: Clinical Significance
Multifocal bone infarcts are a marker for systemic avascular necrosis and indicate the need to investigate for underlying risk factors, particularly sickle cell disease, Gaucher's disease, corticosteroid use, and other thrombotic or embolic conditions. 1
Primary Diagnostic Implications
When bone infarcts are multifocal, they are usually accompanied by multiple foci of epiphyseal avascular necrosis, making them a sentinel finding for widespread vascular compromise rather than an isolated event 1. This pattern occurs in over half of all bone infarct cases, transforming what might appear as a localized problem into a systemic disease marker 1.
Key Clinical Associations
The presence of multifocal bone infarcts should trigger immediate investigation for:
Sickle cell disease: This is the most common underlying condition, where bone infarcts result from sequestration of red blood cells in bone marrow causing vaso-occlusive crises 2, 3. In sickle cell populations, multifocal involvement is particularly common in young children under 6 years of age, with the majority being neonates 4.
Gaucher's disease: The second major cause of multifocal bone infarction 1.
Corticosteroid exposure: A critical iatrogenic risk factor requiring careful medication history 1.
Thrombotic disorders: Including deep vein thrombosis and other hypercoagulable states 5.
Anatomic Distribution Patterns
The main sites of involvement are the distal femur, proximal tibia, and distal tibia 1. However, the distribution pattern provides diagnostic clues:
In patients without sickle cell disease or Gaucher's disease, involvement of the upper limbs and lesions confined to the diaphysis are so rare that their presence should prompt reconsideration of the diagnosis 1.
In sickle cell disease, multifocal patterns can involve craniofacial bones (mandible, orbits, zygomatic arch) in addition to long bones 3, 6.
Pediatric populations show higher rates of multifocal involvement, with studies documenting that 19% of acute osteomyelitis cases in children were actually multifocal, with over half occurring in patients under 6 years of age 4.
Clinical Presentation
Contrary to traditional teaching, bone infarcts cause symptoms in half of cases 1. Patients typically present with:
- Severe bone pain that may mimic osteomyelitis 2, 5
- Fever (particularly in sickle cell vaso-occlusive crises) 5
- Local tenderness and inability to bear weight 5
- Periosteal reaction on imaging, which may be the first and only radiographic change 1
Critical Diagnostic Workup
When multifocal bone infarcts are identified, the following systematic evaluation is mandatory:
Imaging Protocol
MRI is diagnostic and consistently shows typical features, in principle obviating the need for other investigations 1. The unenhanced T1 fat-saturated sequence is particularly valuable for differentiating bone infarcts from osteomyelitis 2.
Whole-body imaging should be performed to identify all sites of involvement, as silent lesions may be present 4.
Standard radiographs are initially normal, then show typical high-density lesions in the center of the marrow cavity with periosteal reaction 1.
Laboratory Investigation
- Complete blood count with hemoglobin electrophoresis (to identify sickle cell disease or trait) 2, 3
- Gaucher's disease screening if clinically indicated 1
- Thrombophilia workup including history of deep vein thrombosis 5
- Medication history focusing on corticosteroid exposure 1
Prognostic Implications
The prognosis of bone infarcts per se is good, with the exception of a very low risk of malignant transformation 1. However, multifocal bone infarcts serve as a marker for systemic avascular necrosis, which may have function-threatening effects at other sites, particularly epiphyseal involvement of major joints 1.
Management Approach
Patients with bone infarcts must be investigated both for known risk factors and for other foci of avascular necrosis 1. This includes:
- Screening for asymptomatic epiphyseal avascular necrosis in major joints (hips, shoulders, knees) 1, 5
- Addressing underlying conditions (sickle cell disease management, discontinuation of corticosteroids if possible) 5
- Monitoring for development of new lesions 1
Important Caveat
Multifocal bone infarcts can be misdiagnosed as multifocal osteomyelitis, particularly in pediatric populations and patients with sickle cell disease 4, 2. The distinction is critical because it determines whether antibiotics are necessary. MRI with T1 fat-saturated sequences showing signal intensity ratios consistent with sequestered red blood cells (rather than inflammatory changes) confirms bone infarction and can prevent unnecessary empirical antibiotic therapy 2.