INTRODUCTION
Histologic exam of bone specimens coupled with bone culture is considered the gold standard
for diagnosis of osteomyelitis (OM) ; however, pre-procedural antibiotic administration and soft
tissue contamination limit utility of bone cultures, leaving histologic diagnosis to stand alone.
The presence of residual OM in an amputation margin results in non-healing wounds and/or
further amputation in 40-47% of patients, and yet few studies have explored the effectiveness of
histologic exam of bone specimens in the diagnosis of OM, there is no standard criteria for
diagnosis, and there is no definition of chronic OM. Lastly, diagnostic concordance among
pathologists is as low as 30% .
In a previous study, we defined and weighted 13 histologic criteria based on the literature (see
Table 1). Using those criteria, we reviewed 385 slides of bone specimens with the following
results:
•
•
•
•
•
•
If the original diagnosis was OM, the criteria based diagnosis was OM
Patients with discordant diagnoses were more likely to fail treatment: 74.39% vs 42.06%;
relative risk = 1.77; p = 0.00001
The majority of diagnostic discordance was chronic OM, where an original diagnosis utilized a
description of chronic OM, but ultimately read as “No Acute Osteomyelitis Identified”
Bone cultures were rarely performed due to pre-procedural antibiotic administration (20%)
Peripheral vascular disease was an independent risk factor for treatment failure
Finally, scores based on weighted criteria suggested potential to indicate the specific type of
OM present, with histologic findings scoring 4 points or less being diagnostic of no
osteomyelitis, and scores ≥6 points indicating a diagnosis of OM
We concluded that descriptive diagnoses of OM do not prompt clinicians to modify treatment,
and chronic OM is under diagnosed.
In this study, we sought to determine if our criteria could improve diagnostic concordance
among pathologists with results similar to our previous study.
CONCLUSION
Histologic Criteria
• The diagnosis of osteomyelitis is difficult. Lack of definitive criteria and definitions for diagnosis
are significant contributors to this diagnostic dilemma. We have developed a histopathological
tool that demonstrates clinical significance in the diagnosis of osteomyelitis in the foot and
ankle, and suggests potential to reduce rates of treatment failure. In addition, our tool has
shown potential to dramatically improve diagnostic concordance among pathologists, even in
the absence of clinical information.
Major (3 points)
- Acute
Neutrophils
Abscess
Fibrinoid Necrosis
• Scores and variations in scores may help pathologists better determine the specific type of
osteomyelitis, and duration of infection.
Bacteria
- Chronic
Sequestrum
Involucrum
Figure 1: Involucrum
Figure 2: Micro-Sequestrum
Intermediate (2 points) Marrow Fibroplasia
Minor (1 point)
Erosion
Remodeling
• Recognizing involucrum and sequestrum is essential to the diagnosis of chronic osteomyelitis.
These are also some of the more difficult histologic features to recognize (Figures 3 & 4).
Granulation Tissue
Chronic Inflammation
• Charcot Arthropathy and chronic/non-healing fracture can have deceptively similar appearances
to chronic osteomyelitis. In difficult cases, clinical history and radiologic findings should be
reviewed before rendering a diagnosis of chronic osteomyelitis.
Destruction
Necrotic Bone
Table 1: Histologic Criteria
Figure 3: Involucrum
Figure 4: Bone Dust
DISCLOSURES & ACKNOWLEDGMENTS
RESULTS
We have no financial or non-financial disclosures.
Agreement:
• Overall concordance among the 6 pathologists was 84%
DESIGN
• Agreement per the specific type of OM was 73% with the greatest disagreement being AOM vs ACOM
• 6 pathologists with experience ranging from 1 to 39 years were recruited to review 35 slides
• All 6 pathologists diagnosed the AOM control as AOM, and the Plasmacytoma as a Neoplasm
• 30 slides from cases of suspected OM of the foot and ankle were selected:
• All 6 pathologists diagnosed the ACOM control as AOM and failed to recognize both involucrum and
micro-sequestrum in this slide (Figures 1 & 2)
₋
₋
₋
All cases were originally diagnosed as “No Acute Osteomyelitis Identified”
Patients with a history of peripheral vascular disease were excluded
5 additional control slides were selected, with original diagnoses as follows:
1. Plasmacytoma
2. Fracture
3. Charcot Arthropathy
4. Acute Osteomyelitis*
5. Acute and Chronic Osteomyelitis*
• Each pathologist was provided with an outline from the previous study, definitions of
histologic criteria, color photocopies and electronic photographs of the histologic criteria, and
a tabulation sheet for each slide.
• Pathologists were asked to mark the presence of each histologic criterion, and make a
diagnosis; however, a diagnosis of OM had to meet the minimum following requirements:
₋
₋
₋
₋
Acute OM (AOM): a minimum of one major acute criterion
Chronic OM (COM): a minimum of one major chronic criterion
Acute and Chronic OM (ACOM): a minimum of one major acute and one major chronic criterion
No OM Identified (NOM): absence of all major criteria
• 2 pathologist diagnosed the Charcot Arthropathy control as COM and one pathologist diagnosed the
Fracture control as COM
Pathologist AOM COM ACOM NOM
The Score:
• The ranges of scores for each diagnosis were often wide;
however, there was a mean 4.38 point difference in score
for each pathologist between a diagnosis of NOM to a
diagnosis of OM (Table 2); p <0.05
A
B
C
D
E
F
• Pathologists with fewer years experience had slightly higher
overall scores
6.38
6.29
6.83
8.8
5.38
5.33
6.33
5.75
8.36
9.38
7.75
4.57
10
11.37
12.2
12
9
7.5
1.75
1.71
3.11
3.8
1.32
1
Table 2: Mean Scores by Diagnosis
The Survey:
• The majority of pathologists said they rarely, if ever, make a definitive diagnosis of COM, and instead use
descriptive diagnoses; however, 100% stated they believed COM was a histologic diagnosis
• 100% felt the criteria would be useful for diagnosing OM in the future
• Pathologists were encouraged to consider a diagnosis other than OM, even if a major
criterion was present.
• 67% stated they would have preferred a lecture in addition to the printed and electronic material prior
to beginning this study
• Pathologists were not given access to any clinical history, radiology or patient outcomes
Patient Outcomes:
• Although similar patient outcomes were seen as in the previous study, such as higher numbers of postprocedural amputations in patients originally diagnosed with NOM but diagnosed with OM during this
study, only 30 patients were examined for this study, as opposed to the 259 patients in the previous
study. Given clinical significance was already demonstrated (p = 0.00001), additional patients were not
added to this study.
• Upon completion of the slide review , each pathologist completed a post-study survey
• Diagnoses from each pathologist were compared for agreement, score, and patient
outcomes, and compared with survey responses
*The control slides of with an original diagnosis of osteomyelitis satisfied the criteria
• Chronic osteomyelitis is one of the primary causes of diagnostic discordance, and is underdiagnosed. We have defined chronic osteomyelitis as the presence of sequestrum and/or
involucrum with marrow fibroplasia, bone remodeling, chronic inflammation, and granulation
tissue; however, this definition must be explored further, and consensus in the pathology
community is needed. In the interim, descriptive diagnoses should include the presence of
involucrum and/or sequestrum when present, and include a differential diagnosis of chronic
osteomyelitis to help clinicians direct further treatment.
Thank you to the 6 pathologists who graciously volunteered as subjects for this study, and the support of the
Pathology Department over the last 2 years of this project .
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