This month's continuing education activity on "The Charcot Foot: Neuropathic Osteoarthropathy" triggers excitatory neurons in the recesses of my clinical memory. As a novice intern in the rheumatology clinic, I called my next patient; I observed that he was able to come from sit-to-stand independently. He walked with a purposeful gait, and a normal stride length and cadence. While walking to the examination room, I was able to time his speed in that defined space, otherwise known as a Timed Up & Go (TUG) Test. He traversed 10 ft in less than 12 seconds, indicating a community ambulatory.1 His dynamic balance and static balance were normal, responding to a "sternal nudge test,"2 in which his balance was "perturbated" by pressing on his sternum while his eyes were closed.
What brings you to the clinic? The patient relayed to me that he was a "golf pro" and was previously able to walk 18 holes, carrying his bag without difficulty. More recently, he noticed the development of arthritic-like symptoms in his ankles at the end of the day. He denied cardiopulmonary disease, hypertension, renal disease, diabetes, or arthritis, as well as trauma, infection, and metabolic, endocrine, or sexually transmitted disease (TIMES). Sexually transmitted diseases are associated with neuropathic joints and arthritis.3 The 6-ft tall patient weighed 230 lb and stated he was reasonably healthy. Range of motion of the triplanar ankle join was restricted in inversion, eversion, dorsiflexion, and plantar flexion. He appeared to have a "rocker-bottom" foot,4 which functioned in the sagittal plane (passing directly from the front to the back during gait) with no lateral or medial motion.
On examination, the patient had normal sensation, 2-point discrimination, vibratory sense, and proprioception. He had normal nerve, artery, vein, empty space, and lymph (NAVEL) by palpation, and his integument was dry and intact. He had mild swelling in both of his ankles but no redness, pain, or increase in temperature. I ordered the obligatory laboratory test with radiograph of the ankles.
My working diagnosis was noninflammatory arthritis of the forefoot and ankle. I prescribed nonsteroidal anti-inflammatory drugs and asked the "pro" to return for my "novice" evaluation after guidance from the attending. In the meantime, I dutifully tracked down the laboratory results and the radiographs.
In presenting these findings, I will review the steps, missteps, and learning moments of the case. One caveat, the diagnostic armamentarium available during my internship was not what it is today.
The patient's blood glucose was 350, sedimentation rate was high, and total leukocyte count was 14,000 with a high neutrophil count. The radiograph of the ankles was consistent with a Charcot joint of the ankle and foot. The patient was diagnosed with diabetes and Charcot joint with coexisting osteoarthritis.
This is a classic example of learning that transitions a student from a novice to a pro. Today more sensitive and specific diagnostic options are available, especially in the imaging sector.
A positive radiograph for Charcot is specific, and when it manifests, the patient is far into the course of the disease. On the other hand, a more highly sensitive test may reveal the disease much earlier but will be negative if the patient does not have the disease. For example, a triple-phase bone scan may show increased activity, but it is highly sensitive to other acute nonspecific inflammatory conditions, and it is not specific to Charcot. To help remember this complicated concept in clinical practice, mnemonics are a useful tool.
In a test that has sensitivity: the mnemonic is SnOut (sensitive test rule out disease). If the test possesses specificity, the mnemonic is Spin (specific test rule in disease).4 In the best case, you would have 2 tests, or even 3, to triangulate the results, otherwise known as combined sensitivity and specificity, which give more diagnostic accuracy.
Assume that all patients have diabetes or are at risk and do not know it; the patient described above was unaware that he had type 2 diabetes. The clinical diagnosis of Charcot foot is primarily based on history and clinical findings but should be confirmed by imaging.5
After my experience in this case, I adopted the practice of screening all clinically indicated diabetic patients by asking if they have had radiographs of their ankles. This practice is corroborated in the literature5,6; however, as discussed, radiographs lack the sensitivity to pick up the disease early but will certainly be positive late in the disease. Moreover, a screening film could serve as a baseline for the patients with risk factors for joint destruction.
And finally, the "6 D's" mnemonic7 has been used commonly to recall the features of Charcot joints: (1) distended, (2) disorganized, (3) dislocated, (4) debris (intra-articular bodies, which can be seen with synovial osteochondromatosis), (5) increased density (sclerosis), and (6) destruction.
Richard "Sal" Salcido, MD
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