Differential Diagnosis

The patient's symptoms of a shingled lesion with hard nodules persisting over a month, followed by an opening and bleeding, suggest a range of possible diagnoses. Here's a categorized differential diagnosis:

• Single Most Likely Diagnosis

  • Basal Cell Carcinoma (BCC): This is a common skin cancer that can present with a hard nodule that eventually ulcerates and bleeds. The description of the lesion's progression fits the typical behavior of BCC, which often starts as a small, shiny bump and can develop into an open sore.

• Other Likely Diagnoses

  • Squamous Cell Carcinoma (SCC): Another form of skin cancer, SCC can also present with a hard nodule that ulcerates and bleeds. It tends to grow more quickly than BCC and can be more aggressive.
  • Keratoacanthoma: A low-grade, or sometimes considered benign, tumor that can resemble SCC but tends to have a more rapid growth phase followed by possible spontaneous resolution. It often presents as a firm, round nodule with a central crater.
  • Pyogenic Granuloma: A benign vascular lesion that can appear as a bleeding polypoid mass, often after minor trauma. It grows rapidly and can bleed easily due to its rich vascular supply.

• Do Not Miss Diagnoses

  • Melanoma: Although less likely given the description, melanoma is a critical diagnosis not to miss due to its potential for metastasis and high mortality if not caught early. Any new or changing skin lesion, especially one that bleeds, should be evaluated for melanoma.
  • Merkel Cell Carcinoma: A rare and aggressive skin cancer that can present as a firm, painless nodule and can grow quickly. It has a high risk of metastasis, making early diagnosis crucial.

• Rare Diagnoses

  • Dermatofibrosarcoma protuberans (DFSP): A rare skin cancer that typically presents as a firm, painless nodule that can grow slowly over years. It rarely metastasizes but can be locally aggressive.
  • Metastatic Skin Cancer: Although rare, skin metastases from internal cancers (like breast, lung, or gastrointestinal cancers) can present as firm nodules that ulcerate and bleed. This would be an unusual presentation for metastatic disease but should be considered in patients with a known history of cancer.
  • Cutaneous lymphoma: Certain types of lymphoma can present with skin lesions, including firm nodules that can ulcerate. This diagnosis is less common but should be considered, especially in patients with a history of lymphoma or immunosuppression.