The ulcer connection
Approximately 50% of diabetic patients with Charcot joint will have an associated plantar ulcer, secondary to the pressure.3 Our patient had a Stage III pressure ulcer—an ulcer with full-thickness skin loss. With Stage III pressure ulcers, there is also damage or necrosis of the subcutaneous tissue, which may extend down to, but not through, the underlying fascia. (For more on staging pressure ulcers, see TABLE.4)
TABLE
Pressure ulcer staging4
| Suspected deep tissue injury | Localized area of discolored intact skin or blood-filled blister. Area may be surrounded by tissue that is painful, firm, mushy, boggy, or warmer/cooler than adjacent tissue |
| Stage I | Nonblanchable erythema of intact skin |
| Stage II | Partial-thickness loss of dermis that presents as a shallow open ulcer with a red/pink wound bed, without slough |
| Stage III | Full-thickness tissue loss; subcutaneous fat may be visible, though bone, tendon, or muscle are not |
| Stage IV | Full-thickness tissue loss with exposed bone, tendon, or muscle. Slough or eschar may be present |
| Unstageable | Full-thickness tissue loss in which the base of the ulcer is covered by slough and/or eschar |
A patient with her share of challenges
Our patient’s podiatrist had diagnosed her with Charcot joint several years prior, and more recently, her primary care physician had put her on antibiotics several times out of concern for cellulitis.
In fact, 2 weeks before we saw her, our patient had started taking antibiotics for a recurrence of infection. Wound cultures which had been sent on the patient were positive for Staphylococcus aureus and Enterococcus, so she began taking linezolid and clindamycin (she was allergic to penicillin and fluoroquinolones).
Worries that she might have a more serious infection prompted a trip to the podiatrist, who performed an MRI, which was questionable for osteomyelitis. The podiatrist then did a bone biopsy to determine if osteomyelitis was present, and provided mechanical debridement for the wound.
While awaiting the biopsy results, the patient developed increasing pain in her foot and developed new drainage from the ulcerated wound, so she sought treatment at our hospital over the weekend. Our pressing concern: Was this an acute process, such as osteomyelitis, or worsening Charcot joint?
The biopsy provided our answer: It was negative for osteomyelitis.
Simple test distinguishes Charcot from infection
A useful test to distinguish Charcot joint from infection in patients who have plantar ulcers is to elevate the affected extremity for 5 to 10 minutes. If swelling and redness persist when the foot is elevated, it is more likely an infectious process. If the swelling and redness resolve, a Charcot process is most likely.
In cases where it’s unclear whether the patient has Charcot joint or an infection, it may be necessary to obtain a synovial or bone biopsy to make the diagnosis.2