Differential Diagnosis for Left Inguinal Lymphadenopathy, Dark Urine, Feverish Feeling, and Chills

Single Most Likely Diagnosis

• Ketamine-induced infection or abscess: The recent injection of subcutaneous ketamine in the abdomen on Friday could lead to an infection, which might cause lymphadenopathy, fever, and chills. The dark urine could be indicative of dehydration or a systemic infection affecting kidney function.

Other Likely Diagnoses

• Urinary Tract Infection (UTI): Symptoms like dark urine, fever, and chills could suggest a UTI, especially if the patient has a history of such infections or underlying urological issues.
• Tick-borne illnesses: Living in a tick-borne area increases the risk of diseases like Lyme disease, Rocky Mountain spotted fever, or ehrlichiosis, which can present with fever, chills, and lymphadenopathy.
• Cellulitis or skin infection: An infection of the skin near the injection site could cause localized lymphadenopathy, fever, and systemic symptoms like chills.

Do Not Miss Diagnoses

• Septicemia or bacteremia: Any infection, especially if related to an injection, could potentially lead to septicemia, which is life-threatening and requires immediate attention.
• Endocarditis: Although less likely without a history of heart disease, any infection could potentially lead to endocarditis, especially if the patient has a pre-existing heart condition.
• Lymphoma or other malignancies: While rare, unexplained lymphadenopathy could be a sign of lymphoma or other cancers, which would be critical to diagnose early.

Rare Diagnoses

• Toxoplasmosis: More common in immunocompromised individuals, but could be considered in the differential for lymphadenopathy and systemic symptoms.
• Brucellosis: If the patient has been exposed to animals or their products, brucellosis could be a rare cause of fever, chills, and lymphadenopathy.
• Histoplasmosis: A fungal infection that could cause lymphadenopathy and systemic symptoms, more common in certain geographic areas or in immunocompromised patients.

Workup

• Complete Blood Count (CBC) to look for signs of infection or inflammation
• Blood cultures to rule out septicemia
• Urinalysis to check for UTI
• Imaging (ultrasound or CT scan) of the abdomen and inguinal area to evaluate the injection site and lymph nodes
• Tick-borne illness testing (e.g., Lyme disease serology) if exposure history is significant
• Consider biopsy of the lymph node if lymphoma is suspected and other causes are ruled out.