**3. Diagnostic process**

## **3.1 Clinical assessment**

In general, the diagnosis and treatment of DFO should be embedded in a standardized multimodal and multidisciplinary approach. The first step is the clinical assessment in terms of the visual presence of infection: new induration, new warmth, new redness, tenderness, purulence and/or altered pain are the main findings. Besides the local signs of infection, there might be systemic repercussions with shivering, lymphangiopathy, and sepsis. Possible additional signs are delayed healing or granulation, putrid smell, or wound vulnerability. These latter symptoms are unspecific and can also occur in other differential diagnoses such as ischemia, acute gout or activated Charcot neuro-arthropathy [11, 12]. The only pathognomonic clinical sign for the external and visual diagnosis of DFO is the presence of fragments of bone discharging from a wound. This is only possible in advanced infections related to ulcers; and it is rare. Often, a DFO is suspected and later confirmed. Large, deep or chronic wounds (persisting for ≥3 months) or red and swollen toes ("sausage toe") raise the suspicion of DFO. Another simple diagnostic approach is the probe-to-bone test. The clinician uses a sterile blunt metal probe to determine, whether bone can be palpated through the diabetic foot ulcer. A negative test does not completely rule out DFO, while a positive test has an acceptable predictive value for deep bone infection [13, 14]. Although needle puncture of deep soft tissue does not reliably predict the results of bone cultures, puncture of the bone itself may be an easy way to obtain bone culture on the ward [15]. When DFO is suspected, two separate positive deep bony microbiological samples showing the same bacteria may sometimes additionally confirm DFO [16]. One or two weeks of "antibioticfree window", before biopsy or surgery, are recommended to avoid false-negative results [17]. In contrast, the microbiological confirmation of DFO is not necessary when the infected area is amputated in toto [18]. All blood tests have no independent values in the mere confirmation of DFO, but might determine the initial, clinical severity of disease on admission.

## **3.2 Imaging**

Upon the clinical suspicion of soft tissue infection and/or chronic ulcer in the polyneuropathy diabetic foot, the clinicians should also always exclude an underlying DFO; at minimum with an X-ray and once at the initial assessment. The X-ray can also be repeated if the lesions are not improving despite adequate therapy, local wound care and off-loading. In a usual approach, the X-ray should be the first imaging, in which signs of DFO can be detected such as osteopenia, periosteal reactions or erosions of the osseous borders [19, 20]. However, the overall sensitivity of the

#### *Diabetic Foot Osteomyelitis: Frequent Pathogens and Conservative Antibiotic Therapy DOI: http://dx.doi.org/10.5772/intechopen.98328*

plain radiography in diagnosing DFO is low. One review cited a pooled sensitivity of 0.54 and a specificity of 0.68 [21]. If the X-ray cannot provide a definitive radiological diagnosis, guidelines frequently recommend MRI for diagnosing DFO with a specificity of 79% and a sensitivity of 93% [22, 23]. However, the MRI is no guarantee of correct radiological diagnosis of DFO [24]. In the MRI, we may find focal signs on T2-weighted images and a loss of signal intensity on T1-weighted images. Furthermore, there is the potential to use short tau inversion recovery sequences (STIR), in which we see high bone signal [25–27]. What is truly beneficial by using the MRI, is the possibility to detect bone marrow edema within 1–2 days after beginning of the bone infection [28, 29]. The MRI is a diagnostic tool for a more accurate diagnostic of DFO. However, we lack clinical data revealing that DFO diagnosed by MRI would have a better outcome than those diagnosed by X-ray and by clinical impression alone. For this latter question, we prospectively followed 390 DFO episodes in 186 adult patients for a median of 2.9 years and performed 318 standard conventional X-rays (median costs 100 Swiss Francs; 100 US\$) and with 47 (12%) MRI scans (median costs 800 US\$). Among them, 18 episodes were associated with positive findings in the MRI only, but lacked bone lesions in the previous X-ray two to three days ago. In the database, the median duration of systemic antibiotics was 28 days for MRI-only episodes and 30 days for X-ray-positive cases and we achieved overall remission in 25% of the MRI-managed cases compared to 27% of the cases with only a standard X-ray imaging on admission. When adjusting for the large case-mix, DFO episodes diagnosed by the MRI had no different remission rates [30].
