Differential Diagnosis for Patient with Extreme Pain after Praluent Injection

Single Most Likely Diagnosis

• Musculoskeletal side effects of Praluent: Praluent (alirocumab) is a monoclonal antibody used to treat high cholesterol. While it is generally well-tolerated, musculoskeletal side effects such as muscle pain and spasms are recognized adverse effects. The patient's description of severe flu-like pain, muscle pain, and headaches without other systemic symptoms like fever or rash aligns with this possibility.

Other Likely Diagnoses

• Influenza or other viral infections: Although the patient denies fever, it's possible for viral infections to present with myalgias (muscle pain) and headaches without fever, especially in patients with chronic conditions like COPD.
• Stress or anxiety reaction: The onset of severe pain following an injection could trigger a stress or anxiety response, exacerbating or contributing to the perception of pain.
• COPD exacerbation: While the patient reports no shortness of breath above her baseline, COPD exacerbations can sometimes present with systemic symptoms like muscle pain and headaches, especially if there's an underlying infection or airway inflammation.

Do Not Miss Diagnoses

• Serum sickness-like reaction: Although rare, some patients can experience a serum sickness-like reaction to monoclonal antibodies, characterized by symptoms such as arthralgias, myalgias, and sometimes rash, which can occur days after the injection.
• Anaphylaxis or severe allergic reaction (delayed onset): While the patient does not have typical symptoms of anaphylaxis like rash, swelling, or difficulty breathing, it's crucial to consider this possibility, especially given the recent administration of a biologic agent.
• Neurological complications: Rarely, injections can cause nerve damage or other neurological issues, which could present with severe pain.

Rare Diagnoses

• Dermatomyositis or polymyositis triggered by the drug: These are rare autoimmune conditions that can be triggered by certain medications, presenting with muscle weakness and pain.
• Hypersensitivity vasculitis: A rare condition that could be triggered by certain drugs, presenting with skin lesions, but also systemic symptoms like arthralgias and myalgias.
• Drug-induced lupus: A rare condition that can be triggered by certain medications, presenting with systemic symptoms including arthralgias, myalgias, and sometimes fever and rash.

Each of these diagnoses should be considered in the context of the patient's overall clinical presentation, medical history, and the temporal relationship to the Praluent injection. A thorough evaluation, including laboratory tests and possibly imaging, may be necessary to determine the cause of the patient's symptoms.