Differential Diagnosis for Acute Onset Severe Hip Pain with Mild Elevation in Uric Acid

Single Most Likely Diagnosis

• Transient Synovitis or Viral Arthritis: This condition is a common cause of acute hip pain, especially in the absence of significant trauma. The improvement in pain by 50% over 5 days could suggest a self-limiting condition. However, the mild elevation in uric acid might also hint at a possible early gout attack, but given the location (hip) and the fact that gout typically affects smaller joints first, transient synovitis is considered more likely initially.

Other Likely Diagnoses

• Gout (First Attack in Hip): Although less common for gout to present in the hip as a first attack, it is still a possibility, especially with the mild elevation in uric acid levels. Gout can occur in any joint, but the hip is an uncommon site for initial presentation.
• Septic Arthritis: This is an infection within the joint space and is a medical emergency. The acute onset of severe pain could be consistent with septic arthritis, especially if there's been any recent trauma, injection, or surgery in the area, or if the patient has a compromised immune system.
• Avascular Necrosis (AVN): This condition involves the death of bone tissue due to a lack of blood supply. It can cause severe hip pain and might be considered, especially if there's a history of steroid use, significant alcohol consumption, or known risk factors for AVN.

Do Not Miss Diagnoses

• Septic Arthritis (Infection): As mentioned, this is a medical emergency that requires prompt diagnosis and treatment to prevent joint destruction and potential systemic infection.
• Osteonecrosis (Avascular Necrosis) with a Fracture: If AVN is present and there's a fracture, this could significantly alter the management and prognosis.
• Malignancy (Bone Tumor): Although less likely, any new onset of severe pain, especially in the context of systemic symptoms like weight loss or fever, should prompt consideration of a bone tumor.

Rare Diagnoses

• Pigmented Villonodular Synovitis (PVNS): A rare condition characterized by swelling and joint pain due to an overgrowth of the joint lining (synovium). It's more common in the knee but can occur in the hip.
• Synovial Chondromatosis: A rare condition where cartilage grows in the synovium, leading to joint pain and swelling.
• Rheumatoid Arthritis (RA) with Hip Involvement: While RA commonly affects smaller joints, it can involve larger joints like the hip, especially in more severe or late-stage disease.

Each of these diagnoses has different implications for treatment and prognosis, highlighting the importance of a thorough diagnostic workup, including imaging studies and potentially arthrocentesis (joint aspiration), to determine the underlying cause of the hip pain.