A 5-year-old boy is brought to the clinic with a 3-day history of a lump on the left side of his neck. His mother reports he had a mild runny nose last week, but it has since resolved. Yesterday, he developed a fever of 101.5°F and began complaining that his neck hurts when he moves his head. On physical examination, there is a 3-cm, erythematous, warm, and exquisitely tender lymph node in the left submandibular region. There is slight overlying skin edema, but no fluctuance is noted. The oropharynx is clear, and there is no hepatosplenomegaly. There are no lesions or rash on the arms.
Which of the following is the most likely causative organism?
The correct answer is:
D) Staphylococcus aureus
The patient is presenting with acute unilateral cervical lymphadenitis. In children, this is most commonly caused by pyogenic bacterial infections, specifically Staphylococcus aureus and Streptococcus pyogenes (Group A Strep). The presentation is typically rapid over a few days, involving a single, large (>2 cm), warm, erythematous, and very tender node. Fever is often present.
Answer choice A: Bartonella henselae, is incorrect. While Bartonella henselae (cat-scratch disease), causes subacute regional lymphadenopathy, the nodes are usually associated with a distal scratch or papule. The progression is slower, and the nodes are often less acutely toxic or erythematous than those in staphylococcal infections.
Answer choice B: Epstein-Barr virus, is incorrect. Viral lymphadenopathy, the most common cause of lymphadenopathy overall, is usually bilateral, involves multiple nodal groups, and the nodes are typically small, rubbery, and minimally tender.
Answer choice C: Mycobacterium avium-intracellulare, is incorrect. This causes subacute/chronic lymphadenitis. The nodes are typically painless, firm, and develop a characteristic violaceous (purplish) hue over time. They may eventually form a sinus tract but do not present with acute fever and warmth.
Answer choice E: Toxoplasma gondii, is incorrect. Toxoplasmosis typically causes asymptomatic or mildly tender generalized lymphadenopathy, often involving the posterior cervical nodes, and is frequently accompanied by a flu-like illness.
Key Learning Point
Acute unilateral cervical lymphadenitis in a child is most often bacterial (S. aureus or S. pyogenes). Management typically involves empiric oral antibiotics, such as clindamycin or cephalexin, that cover these gram-positive organisms. If the mass becomes fluctuant despite antibiotics, an ultrasound should be performed to evaluate for an abscess requiring incision and drainage.
