Inguinal lymph node infection or inflammation: This is often due to a bacterial or viral infection in the lower extremities, genital area, or anal region, which drains into the inguinal lymph nodes. The proximity of these nodes to common sites of infection makes this a common cause.

Sexually Transmitted Infections (STIs): Conditions like syphilis, gonorrhea, and chlamydia can cause inguinal lymphadenopathy. The lymph nodes may become enlarged as the body responds to the infection.
Skin infections or ulcers: Infections of the skin in the lower limbs, such as cellulitis or ulcers, can lead to enlargement of the inguinal lymph nodes as the body fights off the infection.
Viral illnesses: Certain viral illnesses, including mononucleosis and HIV, can cause generalized lymphadenopathy, which may include the inguinal nodes.

Malignancy (lymphoma or metastatic cancer): Although less common, it is crucial not to miss a diagnosis of lymphoma or metastatic cancer to the inguinal lymph nodes, as these conditions require prompt and specific treatment. Cancers such as melanoma, or those originating in the genital or anal areas, can metastasize to these nodes.
Tuberculosis: TB can cause lymphadenopathy, including in the inguinal nodes, especially in individuals from or traveling to areas where TB is prevalent. It's a critical diagnosis to consider due to its public health implications and the need for specific treatment.

Cat-scratch disease: Caused by Bartonella henselae, this condition can lead to lymphadenopathy, including in the inguinal nodes, following a cat scratch or bite.
Filariasis: In endemic areas, filarial infections can cause lymphadenopathy and other lymphatic symptoms, including in the inguinal region.
Autoimmune disorders: Certain autoimmune conditions, such as rheumatoid arthritis or systemic lupus erythematosus, can rarely cause lymphadenopathy, although this is less common in the inguinal nodes compared to other areas.