Inguinal lymphadenitis: This is an inflammation of the lymph nodes in the groin area, often caused by a bacterial or viral infection. It's the most common cause of a swollen lymph node in the groin due to its exposure to various pathogens from the lower limbs and genital area.

Sexually Transmitted Infections (STIs): STIs such as syphilis, gonorrhea, or chlamydia can cause lymphadenopathy in the groin area. The presence of other symptoms like genital ulcers, discharge, or pain can help in diagnosing these conditions.
Cellulitis or skin infections: Infections of the skin or soft tissues in the lower limbs can lead to swollen lymph nodes in the groin as the body responds to the infection.
Fungal infections: Fungal infections like athlete's foot or jock itch can spread and cause lymphadenitis in the groin area.

Lymphoma: Although less common, lymphoma (cancer of the lymphatic system) can present with swollen lymph nodes. It's crucial to consider this diagnosis, especially if the lymphadenopathy is persistent, painless, and accompanied by systemic symptoms like weight loss or fever.
Tuberculosis: TB can affect any part of the body, including the lymph nodes. It's more likely in individuals with a history of exposure or those with compromised immune systems.
HIV: Human Immunodeficiency Virus infection can cause persistent generalized lymphadenopathy. Early diagnosis is critical for the management and treatment of HIV.

Cat-scratch disease: Caused by Bartonella henselae, this disease can lead to lymphadenopathy, typically after a cat scratch or bite. It's more common in children and individuals who are frequently around cats.
Toxoplasmosis: This parasitic infection can cause lymphadenopathy, especially in immunocompromised individuals or those who have ingested undercooked meat or contaminated water.
Kikuchi disease: A rare form of lymphadenitis, often presenting with cervical lymphadenopathy but can occasionally involve inguinal nodes, typically in young women. It's self-limiting but can mimic more serious conditions.