Differential Diagnosis for Numbness and Soreness in the Leg Following Zepbound Injection

Single Most Likely Diagnosis

• Injection Site Reaction: The symptoms described, such as the presence of a fleshy, sore knot at the injection site, soreness radiating downward, and difficulty ambulating due to heel pain, are consistent with a localized reaction to the Zepbound injection. The temporal relationship between the injection and the onset of symptoms supports this diagnosis.

Other Likely Diagnoses

• Neuropathic Pain: The numbness, especially severe at night, and needle-like pricking sensations could indicate neuropathic pain, possibly related to the injection affecting nearby nerves.
• Musculoskeletal Injury: The difficulty in ambulating and the specific mention of inability to put pressure on the heel could suggest a musculoskeletal issue, such as a strain or minor fracture, exacerbated or caused by the injection or subsequent activities.
• Vasculitis or Thrombophlebitis: Although less common, an inflammatory reaction affecting blood vessels (vasculitis) or a blood clot in a vein (thrombophlebitis) near the injection site could cause the described symptoms, including soreness and difficulty walking.

Do Not Miss Diagnoses

• Deep Vein Thrombosis (DVT): While the symptoms might not fully align with a classic DVT presentation, any condition affecting the leg, especially with recent onset of soreness and difficulty walking, warrants consideration of DVT due to its potential for severe complications, including pulmonary embolism.
• Nerve Damage: Direct damage to nerves from the injection could lead to the described numbness and pain. Early recognition and management are crucial to prevent long-term sequelae.
• Infection: Although the presence of a "fleshy, sore knot" might suggest a reaction rather than infection, any injection site can potentially become infected, and such infections can be serious.

Rare Diagnoses

• Complex Regional Pain Syndrome (CRPS): This condition, characterized by intense burning or aching pain in the hands or feet after an injury, could be considered if the pain and numbness persist and are disproportionate to the expected reaction from the injection.
• Eosinophilic Fasciitis: A rare condition characterized by inflammation of the fascia, which could potentially be triggered by an injection, leading to skin thickening, pain, and limited mobility of the affected limb.