Can you diagnose it?
Q. An otherwise healthy 16-month-old boy 👶 presented with initial chief complaint of a “red, 😡 angry rash” on the right knee. The patient’s mother 👩 noticed the erythematous reaction during a diaper change on the morning of the visit but denied any noticeable erythematous rash, pyrexia, or skin markings on the day before the office visit. The patient exhibited no signs of distress and no apparent guarding while walking. Patient’s medical history revealed no allergies, no medication, and no changes in food or environment. It also included no recent hospitalizations, except when he was previously treated for an upper respiratory infection 4 months prior. On examination the patient’s right knee had a warm, non purulent erythema with an irregular border over the anterior aspect. There were visible striations of petechiae noted arising from the right knee, extending up into the posterior torso and the knee was painful to palpation. And there were no signs of insect bites, scratches, or trauma noted on observation. Over hours the patient's symptoms had progressed to warm nonpurulent erythema with irregular striations over the abdomen, torso, and bilateral knee. Tests 📝 ordered at the hospital included complete blood count, microspecimen, and basic metabolic panel along with a plain film radiograph of the right knee. The results were indicative of the presence of an acute infection. The plain radiograph report of the right knee indicated a mild, nonspecific radioopaque stranding 40 mm thick immediately anterior to the knee, with no evidence of right knee joint effusion. What is your differential diagnosis & most probable diagnosis??
