Differential Diagnosis

The patient presents with a combination of symptoms including a lesion on the back, painful lumps on the forearm, and elevated liver enzymes. Here's a categorized differential diagnosis:

• Single Most Likely Diagnosis

  • Sebaceous Cyst for the back lesion: The description of the lesion starting as a blackhead and becoming enlarged and pimple-like after manipulation, along with the physical examination finding of a sebaceous cyst, makes this the most likely diagnosis for the back lesion.
  • Lipoma or Epidermoid Cyst for the forearm lumps: The fluctuating size and tenderness of the lumps could suggest a benign growth such as a lipoma or epidermoid cyst, especially given a previous doctor's assessment as "normal."
  • Alcoholic Liver Disease or Non-Alcoholic Fatty Liver Disease (NAFLD) for elevated liver enzymes: Despite the patient's denial of alcohol consumption, the pattern of elevated GGT over several years could suggest liver disease. NAFLD is also a possibility given the absence of other clear causes for liver enzyme elevation.

• Other Likely Diagnoses

  • Infected Sebaceous Cyst for the back lesion: The history of manipulation and current soreness could indicate an infected sebaceous cyst.
  • Neuroma for the forearm lumps: The description of shock-like pain radiating through the arm could suggest a neuroma, although this is less common.
  • Fatty Liver of Other Etiologies for elevated liver enzymes: Other causes of fatty liver, such as metabolic syndrome or certain medications, could also be considered.

• Do Not Miss Diagnoses

  • Skin Cancer (e.g., basal cell carcinoma, squamous cell carcinoma) for the back lesion: Although less likely, any skin lesion that changes or grows should be evaluated for malignancy.
  • Nerve Tumor or Sarcoma for the forearm lumps: While rare, these conditions could present with similar symptoms and would have significant implications for treatment and prognosis.
  • Viral Hepatitis or Autoimmune Hepatitis for elevated liver enzymes: These conditions can cause elevated liver enzymes and have important implications for treatment and management.

• Rare Diagnoses

  • Dermatofibrosarcoma protuberans for the back lesion: A rare skin cancer that could present as a growing lesion.
  • Neurofibroma for the forearm lumps: Part of neurofibromatosis type 1, which could explain the nerve-like pain.
  • Wilson's Disease or Hemochromatosis for elevated liver enzymes: Rare genetic disorders that affect liver function and could cause elevated liver enzymes.