Differential Diagnosis

• Single most likely diagnosis
  • Septic Arthritis: The patient's symptoms, including joint pain, erythema, subjective fever, and pain with passive range of motion, are highly suggestive of septic arthritis. The fact that the patient recovered well after the initial misdiagnosis also supports this diagnosis, as prompt treatment of septic arthritis can lead to full recovery.
• Other Likely diagnoses
  • Reactive Arthritis: The initial diagnosis made by the partner, reactive arthritis is a possible consideration given the patient's symptoms of joint pain and recent viral infection. However, the presence of erythema and pain with passive range of motion makes septic arthritis more likely.
  • Paronychia: The patient was diagnosed with paronychia by the partner, which is a possible diagnosis given the erythema and pain in the finger. However, this does not explain the patient's other symptoms, such as shoulder and toe pain.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Osteomyelitis: Although less likely, osteomyelitis is a serious infection of the bone that can present with similar symptoms to septic arthritis. Missing this diagnosis could lead to serious complications, including bone destruction and sepsis.
  • Endocarditis: The patient's symptoms of fever, nausea, and joint pain could also be indicative of endocarditis, a serious infection of the heart valves. Although less likely, this diagnosis should not be missed due to its high mortality rate if left untreated.
• Rare diagnoses
  • Rheumatic Fever: A rare but possible diagnosis, rheumatic fever can present with joint pain, fever, and erythema. However, this diagnosis is less likely given the patient's age and lack of other symptoms, such as carditis or chorea.
  • Lyme Arthritis: Although rare, Lyme arthritis can present with joint pain and erythema, especially if the patient has a history of tick exposure. However, this diagnosis is less likely given the patient's lack of other symptoms, such as a characteristic rash or neurological symptoms.