Differential Diagnosis for Small Subcutaneous Nodule in Armpit
- Single Most Likely Diagnosis
- Lipoma: A benign tumor composed of fat tissue, which is the most common soft tissue tumor and can occur in any location, including the armpit. Its presence as a small, movable, and usually painless nodule makes it a likely candidate for a subcutaneous nodule in this area.
- Other Likely Diagnoses
- Cyst (e.g., epidermoid or sebaceous cyst): These are common skin lesions that can occur in the armpit, presenting as firm, movable nodules. They are usually benign but can become infected.
- Abscess or infected sebaceous gland: An abscess is a collection of pus that has built up within the tissue of the body, indicating a local infection. It can present as a painful nodule and is a common issue in areas prone to sweating like the armpit.
- Lymphadenopathy (reactive or infectious): Enlarged lymph nodes can present as nodules in the armpit, often due to infection or inflammation in the area drained by these nodes.
- Hidradenitis suppurativa: A chronic skin condition characterized by recurrent, painful nodules and abscesses in areas of the body with apocrine sweat glands, such as the armpits.
- Do Not Miss Diagnoses
- Metastatic disease (e.g., breast cancer): Although less common, a nodule in the armpit could be a sign of metastasis from a nearby cancer, such as breast cancer. Early detection is crucial for treatment and prognosis.
- Lymphoma: Both Hodgkin and non-Hodgkin lymphoma can present with lymphadenopathy, which might be noticed as a nodule in the armpit. Given the potential severity of lymphoma, it is a critical diagnosis not to miss.
- Cat-scratch disease: Caused by Bartonella henselae, this infection can lead to lymphadenopathy, typically in the area near the site of the cat scratch, which could be the armpit if the scratch occurred on the arm.
- Rare Diagnoses
- Dermatofibrosarcoma protuberans: A rare skin cancer that can present as a firm nodule, often in the trunk but potentially in the armpit area.
- Neurofibroma: A benign nerve sheath tumor that can occur as a solitary nodule or as part of neurofibromatosis type 1. It's less common in the armpit but should be considered in the differential diagnosis, especially in patients with a history of neurofibromatosis.
- Pilomatrixoma: A rare, benign skin tumor that originates from the hair follicle matrix and can present as a firm, sometimes painful nodule, although it's more common in the head and neck area.