A 24-year-old man comes to the urgent care clinic due to painful swelling in his left groin. The patient noticed the swelling 2 days ago, and it has progressively become more tender and painful. He has no chronic medical conditions, but he recently sustained a puncture wound to the sole of his left foot. Physical examination shows an enlarged, tender, and nonfluctuant left inguinal lymph node with erythematous overlying skin. There is a small puncture wound on the sole of the left foot, which expresses pus upon mild pressure. Which of the following histologic findings is most likely responsible for this patient's groin mass?

Question

A 24-year-old man comes to the urgent care clinic due to painful swelling in his left groin.  The patient noticed the swelling 2 days ago, and it has progressively become more tender and painful.  He has no chronic medical conditions, but he recently sustained a puncture wound to the sole of his left foot.  Physical examination shows an enlarged, tender, and nonfluctuant left inguinal lymph node with erythematous overlying skin.  There is a small puncture wound on the sole of the left foot, which expresses pus upon mild pressure.  Which of the following histologic findings is most likely responsible for this patient's groin mass?

Quizplus · Accepted Answer

This patient sustained a puncture wound and subsequently developed inflammatory lymphadenopathy in a draining lymph node, suggesting bacterial infection with lymphadenitis. Lymph nodes serve as sentinel sites for generation of the adaptive immune response. Large, unprocessed foreign antigens are displayed by follicular dendritic cells in the draining lymph node. B cells recognize, bind to, and process the large antigens into smaller peptides that can be displayed on major histocompatibility II receptors to naïve T cells. T cells subsequently differentiate into T-helper cells and secrete cytokines that promote the survival and proliferation of the antigen-specific B cells, leading to the generation of germinal centers. Germinal centers are the sites where B cells compete for survival based upon the ability to bind with high affinity to a foreign antigen. Within these regions, B cells rapidly proliferate and undergo somatic hypermutation (immunoglobulin mutation); this dramatically expands the B cell population capable of binding with high affinity to antigens from the infecting microorganism. Antigen-specific B cells eventually evolve into plasma cells that secrete high affinity antibodies against the invading pathogen. Because the formation of germinal centers results in significant cellular recruitment, patients generally develop lymph node swelling (lymphadenopathy) in the draining lymph node. In addition, the release of large quantities of cytokines frequently causes pain and inflammation in that area. (Choice A) Atypical B-cell proliferation is seen in many forms of lymphoma. However, the lymphadenopathy is usually painless and not associated with erythema because B-cell proliferation without antigen stimulation is not associated with significant inflammatory cytokine release. (Choice B) Granulomatous lymphadenitis can be seen in noninfectious (eg, sarcoidosis) or infectious (eg, tularemia, catscratch disease, cryptococcal) diseases. This patient with a recent puncture wound in the foot and evidence of inflammatory lymphadenopathy in a draining lymph node is far more likely to have a typical bacterial infection than an atypical granulomatous infection. (Choice C) Necrotizing lymphadenitis (eg, buboes) in the groin can be caused by certain serovars of Chlamydia trachomatis. However, this infection is typically seen in tropical and subtropical regions and would not be associated with a recent foot puncture wound. (Choice D) T cells primarily reside in the lymph node paracortex. Paracortical hyperplasia is typically seen with infections primarily dependent on the cell-mediated response (eg, viral infection). Although the paracortical region might expand slightly in bacterial infections, lymphadenopathy is primarily driven by the formation of germinal centers. Educational objective: Germinal centers are the sites where activated B cells proliferate and undergo affinity maturation during generation of a humoral immune response. The formation of multiple germinal centers is typically marked by lymphadenopathy, pain, and inflammation in the affected lymph node due to cellular recruitment and the release of inflammatory cytokines.

A 24-Year-Old Man Comes to the Urgent Care Clinic Due