Differential Diagnosis for a Lump on the Forearm
Single Most Likely Diagnosis
- Lipoma: A benign tumor composed of fat tissue, which is the most common soft tissue tumor. It can appear anywhere on the body, including the forearm, without any preceding trauma.
Other Likely Diagnoses
- Cyst: Such as an epidermoid cyst or a sebaceous cyst, which can form on the forearm. These are usually benign and can appear without any history of injury.
- Abscess: A collection of pus that can form as a result of a bacterial infection. It might not always be associated with an apparent injury but could be related to a minor, unnoticed trauma or infection.
- Hematoma: Although less likely without a history of trauma, a small, unnoticed injury could lead to a hematoma, which is a collection of blood outside of blood vessels.
Do Not Miss Diagnoses
- Soft Tissue Sarcoma: Although rare, sarcomas can present as a lump on the forearm. Missing this diagnosis could be catastrophic due to the potential for malignancy and the need for early intervention.
- Infectious Diseases (e.g., Mycobacterial or Fungal Infections): Certain infections can cause lumps or nodules on the skin, including the forearm. These might not be immediately life-threatening but require specific treatment to prevent complications.
- Metastatic Disease: In rare cases, a lump on the forearm could be a metastasis from a primary cancer elsewhere in the body. This would be particularly concerning in patients with a known history of cancer.
Rare Diagnoses
- Neurofibroma: A benign nerve sheath tumor that can occur in individuals with or without neurofibromatosis. It's less common but could present as a lump on the forearm.
- Dermatofibroma: A small, hard bump on the skin that typically develops following a minor injury, but can occasionally appear without a known cause.
- Panniculitis: Inflammation of the subcutaneous fat, which can cause lumps or nodules under the skin. This condition has various causes, including autoimmune diseases and infections.