Differential Diagnosis for Post-Interscalene Block Brachial Neuralgia

Single Most Likely Diagnosis

• Post-Interscalene Block Brachial Plexus Injury: This is the most likely diagnosis given the context of the question. Interscalene blocks are known to carry a risk of nerve injury, which can lead to brachial neuralgia. The proximity of the block to the brachial plexus and the potential for direct nerve trauma or local anesthetic toxicity makes this a common complication.

Other Likely Diagnoses

• Complex Regional Pain Syndrome (CRPS): This condition can develop after any form of trauma, including needle-related injuries from nerve blocks. Symptoms such as pain, swelling, and changes in skin temperature can mimic or complicate the diagnosis of brachial neuralgia.
• Infection or Abscess: Although less common, infection at the site of the block or an abscess formation can cause pain and neurological symptoms, mimicking neuralgia.
• Hematoma: Bleeding at the site of the block can compress nerves, leading to pain and neurological deficits.

Do Not Miss Diagnoses

• Epidural or Spinal Hematoma: Although rare, these conditions can lead to severe neurological deficits, including paralysis, and are medical emergencies. The risk, though small, necessitates consideration in the differential diagnosis.
• Intravascular Injection of Local Anesthetic: This can lead to systemic toxicity, affecting the central nervous and cardiovascular systems, and is potentially life-threatening.
• Pneumothorax: Given the proximity of the interscalene space to the lung, a pneumothorax could occur, especially if the needle penetrates the pleura. This is a medical emergency.

Rare Diagnoses

• Neuropraxia or Axonotmesis: These are forms of nerve injury that can occur from the block but are less common than other complications. They represent different degrees of nerve damage.
• Systemic Toxicity from Local Anesthetics: While more commonly associated with intravascular injection, systemic toxicity can also occur from absorption of local anesthetics, though this is rare with current formulations and dosing guidelines.
• Nerve Root Avulsion: A severe form of nerve injury where the nerve root is torn from the spinal cord, which is extremely rare but can occur with traumatic injuries, including those from medical procedures.