Differential Diagnosis for a Painful Nodule
Single Most Likely Diagnosis
- Infected Cyst or Abscess: A painful nodule is often indicative of an infected cyst or abscess, which is a common and likely diagnosis given the presentation of pain, which is a hallmark of infection.
Other Likely Diagnoses
- Furuncle or Carbuncle: These are infections of the hair follicle that can present as painful nodules, often caused by Staphylococcus aureus.
- Epidermoid Cyst: While typically not painful unless infected, an epidermoid cyst can become inflamed and painful if it ruptures or becomes infected.
- Pilar Cyst: Similar to epidermoid cysts, pilar cysts can become painful if they rupture or become infected.
Do Not Miss Diagnoses
- Malignancy (e.g., Squamous Cell Carcinoma): Although less common, a painful nodule could be a sign of malignancy, especially if it's growing, bleeding, or doesn't heal. Missing a diagnosis of skin cancer could have severe consequences.
- Necrotizing Fasciitis: A severe infection that can start as a painful nodule but rapidly progresses, requiring immediate medical attention to prevent severe morbidity and mortality.
Rare Diagnoses
- Erythema Induratum: A rare condition characterized by recurrent painful nodules on the legs, often associated with tuberculosis.
- Nodular Vasculitis: A form of vasculitis that presents with painful subcutaneous nodules, typically on the legs.
- Sarcoidosis: Can present with painful nodules, although this is less common than the pulmonary or dermatological manifestations without pain.