Chronic Charcot neuro-osteoarthropathy of the midfoot
The above described findings are those of chronic Charcot arthropathy of the midfoot. No definite MRI evidence of osteomyelitis.
The main differential diagnosis of Charcot's neuro-osteoarthopathy (CN) is diabetic foot osteomyelitis (DFO). Is this diabetic foot infected or not? This is the critical question to answer as both Charcot neuropathy and osteomyelitis can be potentially limb-threatening complications of diabetic neuropathy although with different management protocols. In diabetic foot, it is always difficult at the initial presentation to differentiate between CN and DFO. Moreover, patients with DFO are unlikely to be feverish and not uncommonly lack the local manifestations of wound infection!
Detailed history, physical examination and laboratory investigations as well as imaging is required to reach an almost certain diagnosis.
Almost all diabetic foot osteomyelitis occurs secondary to an infected ulcer, so tracking the foot ulcer and the sinus tract to a likely weight bearing bone with bone marrow edema signal is virtually diagnostic of osteomyelitis. CN usually affects the midfoot with bone destruction whereas the DFO affects the pressure points or the weight-bearing bones as toes of the forefoot or the metatarsal heads or rarely the calcaneus or the cuboid in the rocker-bottom deformity.
Osteomyelitis: periosteal reaction, cortical destruction with bony erosion, new bone formation, bone sclerosis with or without erosion. Sequestrum, involucrum or cloacae.
Charcot neuro-osteoarthropathy: usually joint fragmentation and dislocation as well as non-specific changes with periosteal reaction, bone destruction or traumatic fractures.
Osteomyelitis: Low focal signal intensity on T1-weighted images with high signal on T2-weighted images and STIR sequences usually in a weight-bearing bone (toes, metatarsal heads, or rarely the calcaneus and rocker-bottom cuboid bone). An adjacent skin ulcer with tracking sinus tract through to the bone lesion is a must for a confident diagnosis. Cortical disruption, or adjacent soft-tissue inflammation or edema are secondary changes. A bony abscess with marginal enhancement is a definite criterion for DFO with no further assessment required.
Charcot neuro-osteoarthropathy: Predominant midfoot involvement, joint deformity or subluxation with bony debris, altered bone marrow signal of the subchondral bone with low signal intensity on both T1 and T2-WI with osteosclerosis and subchondral cyst-like lesion. Bone marrow edema which is likely periarticular. Intact overlying skin although may be edematous.