Differential Diagnosis for Limited Arm Mobility

The patient's inability to lift their arm above their head without bending it at 90 degrees suggests a range of potential diagnoses related to musculoskeletal or neurological issues. Here's a categorized differential diagnosis:

• Single Most Likely Diagnosis

  • Adhesive Capsulitis (Frozen Shoulder): This condition is characterized by stiffness and pain in the shoulder joint, leading to limited mobility. The need to bend the arm at 90 degrees to lift it above the head is a common presentation, as it allows the patient to use other muscle groups to compensate for the restricted movement in the shoulder.

• Other Likely Diagnoses

  • Rotator Cuff Injury: Injuries to the rotator cuff muscles or tendons can lead to pain and weakness, making it difficult to lift the arm normally. Bending the arm at 90 degrees may help reduce the strain on these muscles and tendons.
  • Shoulder Impingement Syndrome: This condition, where the shoulder blade puts pressure on the underlying soft tissues when the arm is lifted, can cause pain and limit movement, leading to compensatory strategies like bending the arm.
  • Bursitis or Tendinitis: Inflammation of the bursae or tendons around the shoulder can cause pain and stiffness, potentially limiting the range of motion and leading to similar compensatory movements.

• Do Not Miss Diagnoses

  • Neurological Conditions (e.g., Stroke, Radiculopathy): While less common, neurological conditions affecting the nerves that control the arm can lead to weakness or paralysis, necessitating compensatory movements. Missing these diagnoses could have significant consequences.
  • Bone Fracture or Dislocation: Acute injuries to the shoulder or arm can cause severe pain and limit mobility, sometimes leading to unusual movement patterns as the patient tries to minimize discomfort.

• Rare Diagnoses

  • Polymyalgia Rheumatica: An inflammatory condition that affects the muscles, particularly around the shoulders, leading to stiffness and pain, which might result in limited mobility.
  • Amyotrophic Lateral Sclerosis (ALS): A progressive neurological disease that affects nerve cells in the brain and spinal cord, leading to loss of muscle control. Early stages might present with subtle changes in movement patterns due to muscle weakness.
  • Muscular Dystrophy: A group of inherited disorders characterized by muscle weakness and loss of muscle mass, which could potentially lead to unusual movement patterns as the disease progresses.

Each of these diagnoses has a different set of implications for treatment and management, emphasizing the importance of a thorough clinical evaluation to determine the underlying cause of the patient's symptoms.