Differential Diagnosis for 27-year-old Female with Fever, Bilateral Leg Tenderness, and Stiff Legged Gait

Single Most Likely Diagnosis

• Septic Arthritis: This condition is characterized by joint inflammation due to a bacterial or fungal infection, which could explain the fever, joint tenderness, swelling, and stiff legged gait. The acute onset and the involvement of multiple joints (ankle and knee) make this a plausible diagnosis.

Other Likely Diagnoses

• Osteomyelitis: An infection of the bone, which could cause leg tenderness, fever, and swelling. The symptoms could be consistent with an infection in the bones of the lower extremities.
• Cellulitis: A bacterial skin infection that can cause redness, swelling, and tenderness, which might explain the leg tenderness and swelling, although the joint involvement might suggest a deeper infection.
• Lyme Disease: Caused by a tick-borne bacterium, it can lead to fever, joint pain, and swelling, particularly in the knees. The bilateral involvement and the presence of fever could support this diagnosis, especially if the patient has been exposed to ticks.

Do Not Miss Diagnoses

• Deep Vein Thrombosis (DVT): Although less likely given the bilateral and joint-specific symptoms, DVT can cause leg swelling and tenderness. Missing this diagnosis could be fatal due to the risk of pulmonary embolism.
• Neisseria gonorrhoeae: A sexually transmitted infection that can cause septic arthritis, particularly in young, sexually active individuals. It's crucial to consider this due to its potential for severe consequences if not treated promptly.
• Meningococcemia: A severe infection caused by Neisseria meningitidis, which can present with fever, rash, and limb pain. Although rare, it's critical to diagnose early due to its high mortality rate.

Rare Diagnoses

• Ehlers-Danlos Syndrome: A group of disorders that affect connective tissues supporting the skin, bones, blood vessels, and many other organs and tissues. While it could explain joint issues, it's less likely to present acutely with fever and bilateral leg tenderness.
• Sarcoidosis: An inflammatory disease that can affect multiple parts of the body, including the joints. It might cause joint pain and swelling but is less common and would typically have other systemic symptoms.
• Henoch-Schönlein Purpura (HSP): A form of vasculitis that affects blood vessels and can cause joint pain, fever, and rash. Although it could fit some of the symptoms, the absence of a characteristic rash makes it less likely.