We received a number of great responses to part 1 of this case presentation in the eTalk thread on this topic, and as many of you noted, there are a number of possibilities to include in the differential diagnosis for this challenging patient.
Considering the significant pain symptoms that the patient demonstrated, and in concern that the patient may have ruptured through his TAL site, the decision was made, as many of you suggested, to obtain an MRI of the right lower extremity to assess the integrity of the Achilles tendon following the TAL and to evaluate the osseous and soft tissue structures in the area of the patient’s pain.
See below the MRI findings:
The TAL site demonstrated full healing with no residual tenosynovitis noted on the MRI. The MRI findings were perplexing –the patients pain symptoms were predominantly around the ankle, and he demonstrated no pain, swelling or erythema in the area of the 5th metatarsal base or along the lateral aspect of his foot. However, considering these unusual findings consistent with potential osteomyelitis at the 5th metatarsal –despite previous clear margins a year ago—the decision was made to bring the patient to the operating room to perform a bone biopsy of the 5th metatarsal base as well as to obtain deep wound cultures to evaluation for the possibility of infection both in the soft tissues as well as in the bone.
The bone biopsy proceeded uneventfully, and the specimens were sent to the BAKO pathology laboratory for both pathologic evaluation as well as culture, sensitivity and gram stain. See below for the histopathologic slide from the bone specimen.
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Lamellar bone with inflammatory changes consistent with chronic osteomyelitis |
The pathology report demonstrated osseous changes consistent with chronic osteomyelitis and the bone culture and deep wound cultures demonstrated MRSA that was sensitive to clindamycin.
A PICC was then placed, and the patient was referred to a local infectious disease specialist for the management of parenteral antibiotics. Once starting on the antibiotic therapy, his pain symptoms largely resolved.
Discussion:
We have all heard the adage: “When you hear hoof-beats, think horses”. However, in this case, the most obvious source of the patient’s ankle pain symptoms seemed to be related to the recent TAL. He was not demonstrating symptoms in the area of the 5th metatarsal base and therefore the MRI findings suggestive of osteomyelitis were unexpected. So unexpected were they, in fact, that I called the radiologist for a re-read and to discuss the findings. While my clinical suspicion for osteomyelitis was low, considering the patient’s previous history, I decided that it would be appropriate to perform the bone biopsy, if for no other reason to adequately rule out the potential for bone infection.
There are a number of interesting aspects of this case. Despite having previously demonstrated negative margins following serial debridements a year prior, the patient demonstrated histiopathologic evidence of chronic osteomyelitis, consistent with the MRI findings. This is interesting because had demonstrated no further ulcerations along the lateral aspect of his foot, nor was he demonstrating classic, cardinal signs of infection: rubor, dolor, calor, etc. During his previous osteomyelitis, he had not demonstrated MRSA, but rather MSSA, which was treated with antibiotics per infectious disease recommendations. The progression to MRSA was an interesting twist –especially because he demonstrated sensitivity to clindamycin, which is commonly associated with community acquired MRSA.
MRI has become increasingly useful in the diagnosis of osteomyelitis, and bone biopsy remains the gold-standard for the diagnosis of osteomyelitis, and in this case, it was invaluable in confirming the diagnosis of osteomyelitis to allow for appropriate treatment.
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