Differential Diagnosis for Patient with Left Inguinal Lymphadenopathy

Single Most Likely Diagnosis

• Abscess or Soft Tissue Infection at the Injection Site: Given the recent history of a subcutaneous injection of ketamine in the abdominal fat, the development of mild fever, chills, and worsening symptoms through the day, an abscess or soft tissue infection at the injection site is highly plausible. The proximity of the symptoms to the injection site and the timeline support this diagnosis.

Other Likely Diagnoses

• Lymphangitis or Cellulitis: These conditions could be secondary to the injection, especially if the technique was not sterile or if the patient has a predisposing condition. The presence of lymphadenopathy and systemic symptoms like fever and chills supports this possibility.
• Tick-Borne Illness: Given the patient's exposure to a tick-endemic area, tick-borne illnesses such as Lyme disease, Rocky Mountain spotted fever, or Southern tick-associated rash illness (STARI) could be considered, especially if the patient presents with a rash or other specific symptoms associated with these diseases.

Do Not Miss Diagnoses

• Septicemia or Bacteremia: Although less likely, any infection that leads to septicemia or bacteremia can be life-threatening and requires immediate attention. The presence of fever and chills could indicate a systemic infection.
• Necrotizing Fasciitis: This is a severe infection of the fascia, the tissue that covers muscles, nerves, fat, and blood vessels in the affected area. It is a medical emergency and can be a complication of soft tissue infections, especially if not promptly treated.
• Endocarditis: In patients with pre-existing heart conditions, an infection at the injection site could potentially lead to endocarditis, an infection of the inner lining of the heart chambers and valves.

Rare Diagnoses

• Ketamine-Induced Vasculitis or Allergic Reaction: While rare, an allergic reaction or vasculitis induced by ketamine could potentially cause lymphadenopathy and systemic symptoms.
• Lymphoma or Other Malignancies: Although very rare and less likely given the acute presentation, lymphadenopathy can sometimes be the first sign of lymphoma or other malignancies. However, this would typically not present with such acute systemic symptoms like fever and chills unless there was significant disease progression or an associated infection.