A 56-year-old woman presents to the emergency department complaining of foot pain. She says the bottom of her foot aches, and is hot and red. The pain is worse with walking, but it improves slightly with rest. She has recently started a walking program (two miles three times a week) for weight loss. She has had Type 2 diabetes mellitus for 16 years, and a chronic foot ulcer (seen in the photo), for which she sees a podiatrist. She denies any recent acute trauma, fevers, drainage from the ulcer site, or knee or calf pain.
What is her diagnosis, and how would you acutely manage her condition in the ED? See p. 10.
Diagnosis: Charcot Foot
Charcot foot (also called diabetic neuropathic arthropathy or neuropathic joint) is an uncommon progressive, degenerative condition that affects the joints of the feet. Acute exacerbations are typically self-limited, but can have limb-threatening consequences. Interestingly, Charcot was first described in patients with tertiary syphilis, but is now most commonly seen in patients with diabetes.
Foot problems are a frequent cause of morbidity in diabetic patients; as many as 25 percent develop severe foot or leg problems. Skin ulceration is the most common complication, but bony disease including osteomyelitis and Charcot osteoarthropathy can occur. (Nucl Med Commun 2006;27:745.) Nine percent of all diabetic patients develop Charcot foot (Am Fam Physician 1998;57:2705), which tends to develop in patients with long-standing diabetes (15+ years), but can occur in those as young as 20. (Postgrad Med 1991;89:163.)
Charcot osteoarthropathy is associated with neuropathy, which decreases the body's ability to sense stimuli, including pain. This allows for progressive damage to the joints of the feet secondary to repeated trauma and injury. The exact etiology has not been determined, but in about 50 percent of cases, the condition may develop after sudden trauma (foot fracture, contusion, or sprain). The other half may have a more insidious onset, likely from local repetitive microtrauma. Another school of thought is that the neuropathic condition generates increased blood flow to the extremity, creating a mismatch in bone destruction and synthesis, leading to osteopenia. The condition does, however, develop over weeks to months.
Peripheral neuropathy results in intrinsic foot muscle weakness and ligamentous laxity; this subsequently allows bony subluxation or dislocation and arch collapse. Irritation between the bones occurs when the patient walks, and this initiates degenerative joint disease. As the condition progresses, the foot arch collapses, bones are dislocated, fractures develop from abnormal weight distribution on the foot, and new bony growths protrude on the dorsal foot surface as the body attempts to replace bone loss. In advanced disease, it is not uncommon for the foot to have a rocker-bottom (convex) shape, making walking difficult.
Charcot foot affects the metatarsal, tarsal, and tarsometatarsal (Lisfranc's) joints. Arthropathy of the midfoot is most common (70%), with 15 percent occurring at the forefoot or rearfoot area. Reports of gender predisposition are conflicting (some state a 3:1 male:female predominance). The condition is typically unilateral with only 10 to 25 percent of cases becoming bilateral.
Symptoms and Diagnosis
The symptoms of Charcot foot vary. Patients have mild foot swelling with no deformity or acute onset of profound unilateral warmth, tenderness, erythema, and swelling (from synovial fluid leaking from the joint capsule) of the foot or ankle, which can mimic cellulitis, gout, or deep vein thrombosis. The foot can appear severely deformed (flat or convex midfoot), with crepitous audible or palpable on examination. As many as 75 percent of patients have pain, but the pain is less than expected given their neuropathy. More than one-third of patients will have an associated skin ulcer, which can be concerning for osteomyelitis.
The diagnosis of Charcot osteoarthropathy is typically made with radiographs. Bony destruction, fragmentation, joint subluxation, and bony remodeling are considered radiographic hallmarks of the disease. (Am Fam Physician 1998;57:2705.) In the forefoot, bone resorption can lead to partial or complete loss of the metatarsal heads (“pencil-pointing”). Bone scan and MRI may be used in equivocal cases, but have minimal utility in the ED. White blood cell count and erythrocyte sedimentation rate (ESR) may have some limited value when trying to distinguish an acute Charcot arthropathy from an acute infectious etiology.
The initial treatment of acute Charcot foot is immobilization of the joint. The hope is that by decreasing the gravitational forces on the fragile maligned bony structures, the rate of midfoot arch collapse and disease progression will be stopped and allow for healing. ED placement of a posterior splint to the knee should be sufficient until close outpatient follow-up can be arranged. Patients will then be placed in a more permanent cast, removable boot, or brace for weeks to months, typically with strict non-weight-bearing instructions.
Recent studies have shown that use of weight-bearing casts in the acute phase may be acceptable. (J Bone Joint Surg Am 2008;90: 754.) After the acute phase subsides, patients may be able to return to weight-bearing activities, but may require custom shoes or bracing for months to years. Surgery may be required in more advanced cases. Oral bisphosphonate administration (Diabetes Care 2005;28:1214) and intranasal calcitonin (Diabetes Care 2006;29:1392) may have roles, but have yet to be validated in a large population.
Because many of these patients have diabetes, hyperglycemia and hypoglycemia should be evaluated and treated. Complications of Charcot osteoarthropathy can include callus and ulcer formation in areas of bony prominence. These areas are at risk for secondary infection, and the development of osteomyelitis or septic arthritis. This can lead to severe morbidity and subsequent extremity amputations.
This patient was discharged from the ED with a posterior lower extremity splint, crutches, non-weight-bearing instructions, analgesia, and follow-up with her podiatrist.