What are the differential diagnoses for a patient with persistently elevated Immunoglobulin G4 (IgG4) levels, normocytic anemia, and chronic, non-healing skin lesions with distinctive firm, white borders, in the absence of eosinophilia and with normal Immunoglobulin A (IgA), Immunoglobulin G (IgG), Immunoglobulin E (IgE), and Immunoglobulin M (IgM) levels?

Differential Diagnosis

The patient's presentation is complex, with consistently elevated IGG4 levels, skin sores that fail to heal, and unexplained weight loss. The following differential diagnoses are considered:

• Single Most Likely Diagnosis
  • IGG4-Related Disease (IGG4-RD): Although the patient's symptoms and lab results are consistent with IGG4-RD, the diagnosis is not definitive. The presence of elevated IGG4 levels, skin sores with a firm, whitish border, and fibrosis on biopsy are all consistent with IGG4-RD. However, the patient's lack of response to treatment and the presence of atrophic white patches with small red dots are not typical of IGG4-RD.
• Other Likely Diagnoses
  • Chronic Cutaneous Sarcoidosis: The patient's skin sores, which are circular with a firm, whitish border, and the presence of fibrosis on biopsy, are consistent with chronic cutaneous sarcoidosis. The patient's mild normocytic anemia and unexplained weight loss also support this diagnosis.
  • Lymphoma: The patient's unexplained weight loss, mild normocytic anemia, and the presence of fibrosis on biopsy raise the possibility of lymphoma. A lymph node biopsy or imaging studies may be necessary to rule out this diagnosis.
  • Infectious Disease (e.g., Leishmaniasis, Cutaneous Tuberculosis): The patient's positive test for Filariasis AB IGG4, despite never leaving the United States, is unusual. However, it is possible that the patient has an infectious disease that is causing the skin sores and other symptoms.
• Do Not Miss Diagnoses
  • Cutaneous T-Cell Lymphoma (e.g., Mycosis Fungoides): This diagnosis is important to consider due to the patient's skin sores and unexplained weight loss. A skin biopsy and imaging studies may be necessary to rule out this diagnosis.
  • Systemic Lupus Erythematosus (SLE): Although the patient's symptoms are not typical of SLE, the presence of mild normocytic anemia and unexplained weight loss raise the possibility of this diagnosis. A thorough evaluation, including autoantibody testing and imaging studies, may be necessary to rule out SLE.
• Rare Diagnoses
  • Erythema Induratum: This rare condition is characterized by recurring, painful skin nodules that may leave atrophic scars. The patient's skin sores, which are circular with a firm, whitish border, and the presence of fibrosis on biopsy, are consistent with erythema induratum.
  • Necrobiosis Lipoidica: This rare condition is characterized by skin lesions that are often circular and have a firm, whitish border. The patient's skin sores and the presence of fibrosis on biopsy are consistent with necrobiosis lipoidica.

Recommendations

1. Skin Biopsy: A repeat skin biopsy, including immunohistochemical staining, may be necessary to further evaluate the patient's skin sores.
2. Imaging Studies: Imaging studies, such as a chest X-ray or CT scan, may be necessary to evaluate for lymphadenopathy or other systemic involvement.
3. Autoantibody Testing: Autoantibody testing, including ANA and anti-SSA/Ro, may be necessary to evaluate for SLE or other autoimmune disorders.
4. Infectious Disease Testing: Further infectious disease testing, including blood cultures and serologic testing, may be necessary to evaluate for underlying infections.
5. Lymph Node Biopsy: A lymph node biopsy may be necessary to evaluate for lymphoma or other systemic involvement.
6. Erythropoietin Level: A repeat erythropoietin level may be necessary to evaluate for underlying anemia or other hematologic disorders.
7. IGG4 Level Monitoring: The patient's IGG4 level should be monitored regularly to evaluate for changes in disease activity.