Differential Diagnosis for a 5-year-old with a Painful Bump Under the Arm
- Single most likely diagnosis
- Infected lymph node or lymphadenitis: This is a common condition in children, where a lymph node becomes infected, usually due to a bacterial or viral infection. The presence of a painful bump under the arm without discharge or surrounding erythema could indicate an infected lymph node.
- Other Likely diagnoses
- Cat scratch disease: This is a bacterial infection caused by Bartonella henselae, typically transmitted through a cat scratch or bite. It often presents with a painful lymph node, usually in the axilla, which matches the symptoms described.
- Furuncle or carbuncle: Although less likely without surrounding erythema, a furuncle (boil) or carbuncle (cluster of boils) could present as a painful bump under the arm. These are usually caused by Staphylococcus aureus.
- Hidradenitis suppurativa: This chronic skin condition involves recurrent, painful abscesses and nodules in areas of the body with apocrine sweat glands, such as the axillae. However, it's less common in young children.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Tuberculosis (TB) lymphadenitis: Although less common, TB can cause lymphadenitis, which might present similarly. Given the potential severity and need for specific treatment, it's crucial not to miss this diagnosis.
- Malignancy (e.g., lymphoma): While rare in children, lymphoma could present with lymphadenopathy (enlarged lymph nodes) that might be painful. Early diagnosis is critical for effective treatment.
- Rare diagnoses
- Lipoma or other benign tumors: These could present as a bump under the arm but are typically painless.
- Cystic hygroma or other congenital anomalies: These are rare conditions that could present as a mass in the axillary region but are usually identified earlier in life.
- Actinomycosis: A rare bacterial infection that can cause abscesses or masses in various parts of the body, including the axilla, but this would be an unusual presentation.