Diagnosis of Charcot Foot: An Overlooked Diabetic Consequence
Article Outline
The incidence of type 2 diabetes in the United States and worldwide is increasing on an annual basis. As diabetes becomes increasingly prevalent, nurse practitioners (NPs) will see a greater number of patients affected by uncontrolled blood glucose. Because the majority of care for type 2 diabetics will be provided by primary care providers, the NP should be familiar with physical exam findings seen in clients with uncontrolled diabetes.
One of the complications of uncontrolled diabetes is neuropathic osteoarthropathy or Charcot foot. Charcot foot deformity is the progressive structural change of bones and ligaments caused by injury that goes unrecognized due to neuropathy. Due to loss of pain awareness (nociception), patients continue to bear weight on the affected foot, causing further structural damage. In comparison to diabetic neuropathy, Charcot foot deformity can develop in just weeks.1
Causes of Charcot foot deformity include alcoholic neuropathy, sensory loss from cerebral palsy, tertiary syphilis, leprosy, or other conditions causing the inability to perceive pain. Two thirds of patients with Charcot foot, however, have type 2 diabetes. Many of these patients have obesity associated with their diabetes, increasing the weight exerted on these damaged tissues.
Two mechanisms are believed to be involved: neurotraumatic and neurovascular. Neurotraumatic damage occurs due to loss of nosciception and proprioception. An injury occurs and the patient continues to ambulate due to the inability to perceive the pain. Neurovascular mechanisms include autonomic stimulation of vascular reflexes that cause hyperemia and periarticular osteopenia of the affected bone.2
Early diagnosis and treatment increase the chance for successful outcomes.3 Diagnostic delays for up to 6 months have been reported in retrospective studies. The NP should be aware of the potential adverse consequences from diagnostic delays. Mortality rates associated with diabetic Charcot foot are equal to those associated with diabetic foot ulcers. Unrecognized, untreated Charcot foot deformity can lead to diabetic foot ulcers, osteomyelitis, septic arthritis, or gangrene resulting with amputation.
Trauma is not a prerequisite for the development of Charcot foot, and approximately 50% of patients do not remember any mechanism of injury. Because patients do not mention pain, Charcot foot is missed up to 25% of the time. Because patients often do not seek care for a foot concern, the deformity is often identified during follow-up exams.
During a routine follow-up visit, the NP should inspect the general appearance, symmetry, and skeletal features of the feet. Findings of Charcot foot include feet asymmetry, ankle or foot edema, erythema, and warmth.4 Additional clinical signs of Charcot foot may include joint instability, subluxation or dislocation, bounding pedal pulses, and reduced sensation to monofilament testing. Because of similar clinical findings, diagnoses often confused with Charcot foot include cellulitis, venous thrombosis, gout, and sprains. Figure 1 illustrates edema over the navicular region and the left medial malleolus of the tibia.
Figure 1.
Reduced bone strength and peripheral neuropathies are a result of poor tissue oxygenation. Office assessment of arterial vascular supply is easily performed with Ankle-Brachial Indexes (ABI). The test may be delegated to office personnel who have been trained in the procedure. The test is cost-effective in comparison to vascular imaging studies, as well as accurate. ABIs also identify the patient's chances for healing. The systolic blood pressure should be taken in both arms. The highest reading of the 2 should be used for the calculation. The systolic pressure should then be measured in the lower extremity of concern. A blood pressure cuff is applied above the ankle, and the systolic pressure in either the posterior tibial or dorsalis pedis artery is determined. This may be easier heard with a Doppler than a standard stethoscope. A normal ankle pressure should be slightly greater than, or equal to, the brachial pressure (normal ABI 1.0–1.2). An ABI of 90% or less indicates the presence of peripheral arterial disease. Results can be categorized as mild, moderate, or severe claudication.
Initial destruction of bony tissue may result from fractures, joint dislocations, or both. Plain radiographs can help identify joint effusions, large osteophytes, fractures, bone fragments, and joint misalignment. However, radiographic findings can be normal in the acute phase of Charcot fracture. Magnetic resonance imaging (MRI) or a 3-phase nuclear medicine bone scan can help differentiate between Charcot foot and osteomyelitis. Joint margins are blurred in osteomyelitis compared to clearer margins in Charcot deformity. An Indium-111 leukocyte scan may also help identify an infectious bony process. A venous duplex scan can rule out venous occlusion. Laboratory analysis of joint fluid (arthrocentesis) may detect bone and cartilage fragments and blood. The NP can consult with a radiologist to help determine the best imaging study.
Consideration of Charcot foot deformity as a differential diagnosis is important in providing timely referral to a podiatrist, orthopedist, or a diabetic foot center for specialty care. Until the time of referral, strict non-weight-bearing should be observed, and the foot and ankle should be stabilized. Follow-up in the primary care office should be continued while the patient is waiting for evaluation by a specialist. Vascular and skin assessments should be routinely performed. The NP should provide patient education regarding vascular compromise in both verbal and written format.
References
- Peng H, Swierzewski SJ. Charcot foot: diagnosis, treatment, complications. Healthcommunities.com. May 22 2007. Available at: http://www.podiatrychannel.com/charcotfoot/diagnosis.shtml. Accessed December 16, 2008.
- . Charcot foot: the diagnostic dilemma . Am Fam Physician . 2001;64(9):1591–1599
- . Charcot foot. April 2008 . Available at: http://www.footphysicians.com/footankleinfo/charcot-foot.htm Accessed December 16, 2008.
- . Epidemiology of the Charcot foot . Clin Podiatr Med Surg . 2008;25(1):17–28
PII: S1555-4155(09)00136-6
doi:10.1016/j.nurpra.2009.02.016
© 2009 American College of Nurse Practitioners. Published by Elsevier Inc. All rights reserved.
