The pedal pulse: not always a black and white sign
A 82-year-old man went to the Emergency Department (ED) with a strong acute pain located in the toes of both feet. He was a heavy smoker with a previous myocardial infarction ten years before. Physical Examination showed a distal erythema in both legs, normal temperature and a blue-red color of the skin around the toes and soles. The pedal pulses were palpable. A diagnosis of gout (podagra) was established. The patient had two more visits to the ED. In the third one, a radical surgical procedure had to be implemented..
CLINICAL EVOLUTION: At the second visit one week later the patient continued with a strong pain around the toes, with more erythema now spreading to the ankle. He has no high fever or chills. A second diagnosis of cellulitis was established and the patient started with antibiotics,
In a third visit some days later the erythema was more intense in the left leg, spreading close to the knee.
FINAL DIAGNOSIS: ischemia, Blue-toe syndrome.
The patient was treated with surgery with a partial amputation below his left knee.
ANALYSIS: Diagnosis error related with a cognitive bias ( representation heuristic).
FIRST DIAGNOSIS: Gout. Doctors attending the patient selected the first diagnosis (gout, podagra) based on the representation of erythema always in relation with arthritis and its location over the interphalangeal joints.
We show here a “typical” episode of acute gout with the location over the first metatarsal area:
SECOND DIAGNOSIS: cellulitis. In the second visit the erythema spread around the feet and ankle with a normal skin temperature with palpable pedal pulses and this data discarded the diagnosis of ischemia.
COMMENTS: Pattern recognition diagnosis is based on some ideal models stored in our brain, build after previous encounters with the same entity. Strong pain over the first toe with a temperature increase , brings to mind podagra, but sometimes we have to calibrate our mind if the whole constelation of symptoms and signs can´t be put into our model. A palpable pedal pulse brings to mind a feeling of confidence about a normal vascular anatomy, but there are exceptions as we can see in the blue-toe syndrome produced by cholesterol crystals that block the oxygenation in the small distal arteries.