History of Present Illness (HPI)

The patient is a 65-year-old female with a past medical history of right total knee replacement 7 years ago. She presents with a one-month history of right hip pain, characterized as throbbing and exacerbated by movement, with no radiation, numbness, or tingling. The pain is constant, rated 8/10 at rest and 8/10 currently. Additionally, she complains of a balding spot on the right side of her scalp with persistent itching, allergy symptoms, and nasal congestion over the past month. She also reports right knee pain, which she finds relieved by wrapping her knee with an ace wrap. Two weeks ago, she had a fall onto her left side but reports no direct injury to her right hip or knee.

Differential Diagnosis

• Single Most Likely Diagnosis
  • Osteoarthritis (OA) of the Hip: Given the patient's age, history of joint replacement, and description of hip pain exacerbated by movement, OA is a likely cause. The absence of systemic symptoms such as fever or weight loss and the lack of radiation or neurological symptoms support this diagnosis.
• Other Likely Diagnoses
  • Bursitis or Tendinitis: These conditions could explain the patient's hip pain, especially if it's exacerbated by movement. The recent fall, even though on the opposite side, could have altered her gait, putting additional stress on the right hip.
  • Allergic Reaction or Dermatitis: The itching balding spot on the scalp and allergy symptoms could be related to an allergic reaction or dermatitis, possibly exacerbated by or unrelated to her hip and knee issues.
• Do Not Miss Diagnoses
  • Infection (Prosthetic Joint Infection or Septic Arthritis): Although less likely given the time frame since the knee replacement and the absence of systemic symptoms like fever, an infection must be considered, especially in patients with a history of joint replacement.
  • Fracture: Despite the patient landing on her left side during the fall, a fracture of the right hip or pelvis cannot be ruled out without imaging, especially if there was any indirect trauma or stress to the right hip.
  • Avascular Necrosis (AVN): This is a potential complication in patients with a history of steroid use or significant trauma, which could lead to hip pain.
• Rare Diagnoses
  • Rheumatologic Conditions (e.g., Rheumatoid Arthritis, Lupus): These conditions could explain multiple joint pains, skin symptoms, and possibly the allergic-like symptoms, though they are less common in this age group without a prior diagnosis.
  • Neoplastic Conditions: Although rare, tumors could cause hip pain and should be considered, especially if other diagnoses are ruled out and the pain persists or worsens over time.

Each diagnosis is considered based on the patient's symptoms, history, and potential risks. A thorough physical examination, laboratory tests (including inflammatory markers and possibly autoimmune panels), and imaging studies (such as X-rays or an MRI of the hip) would be essential in narrowing down the differential diagnosis and guiding further management.