How does the diagnosis of osteomyelitis differ in patients with Charcot arthropathy (neuropathic joint)?
Patients with neuropathic arthropathy of Charcot have preexisting joint space destruction, bony fragmentation, and bone marrow edema—findings that would otherwise raise suspicion for osteomyelitis. However, both Charcot arthropathy and osteomyelitis are often coexistent, particularly in patients with advanced diabetes mellitus. Therefore, the diagnosis of osteomyelitis is particularly challenging in these patients. Radiographs are helpful only if they have highly specific signs of infection (e.g., soft tissue gas) or if they show rapid temporal evolution of the osteolysis. MRI diagnosis relies on identifying a skin ulcer that directly extends to the region of bone marrow edema. That is, bone marrow edema without subjacent ulceration most probably reflects neuropathic arthropathy, whereas bone marrow edema subjacent to a skin ulcer most likely reflects osteomyelitis. In this way, MRI is sometimes only marginally better than a careful physical examination in this patient population.