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.
• Other Likely Diagnoses
  • Sarcoidosis: The patient's skin sores, weight loss, and mild anemia are consistent with sarcoidosis. However, the lack of elevated eosinophils and normal IgA, IgG, IgE, and IgM levels make this diagnosis less likely.
  • Chronic Cutaneous Lupus Erythematosus: The patient's skin sores, particularly the circular shape with a firm, whitish border, are consistent with chronic cutaneous lupus erythematosus. However, the lack of other systemic symptoms and normal immunoglobulin levels make this diagnosis less likely.
  • Granuloma Annulare: The patient's skin sores, particularly the circular shape with a firm, whitish border, are consistent with granuloma annulare. However, the presence of fibrosis and fibroblasts on biopsy make this diagnosis less likely.
• Do Not Miss Diagnoses
  • Lymphoma: Although the patient's symptoms and lab results are not strongly suggestive of lymphoma, it is essential to consider this diagnosis due to the potential for severe consequences if missed. A lymph node biopsy or imaging studies may be necessary to rule out lymphoma.
  • Infection (e.g., Mycobacterial or Fungal): The patient's skin sores and weight loss could be indicative of a chronic infection. Although the patient has not responded to broad-spectrum antibiotics, it is essential to consider other infectious agents, such as mycobacteria or fungi.
  • Parasitic Infection (e.g., Leishmaniasis): The patient's positive test for Filariasis AB IGG4, although unlikely given the patient's travel history, raises the possibility of a parasitic infection. Other parasitic infections, such as leishmaniasis, could also be considered.
• Rare Diagnoses
  • Erythema Induratum: This rare condition is characterized by recurring, painful skin nodules, often on the legs. The patient's skin sores, particularly the circular shape with a firm, whitish border, are consistent with erythema induratum.
  • Necrobiosis Lipoidica: This rare condition is characterized by skin lesions, often on the legs, that can be painful and take months to heal. The patient's skin sores, particularly the circular shape with a firm, whitish border, are consistent with necrobiosis lipoidica.

Recommendations

1. Skin Biopsy: Repeat skin biopsies, including a biopsy of a new lesion, to further evaluate the histopathological features and rule out other conditions.
2. Imaging Studies: Consider imaging studies, such as a CT scan or MRI, to evaluate for lymphadenopathy or other systemic involvement.
3. Infectious Disease Workup: Consider a more comprehensive infectious disease workup, including tests for mycobacterial and fungal infections.
4. Lymph Node Biopsy: If lymphadenopathy is present, consider a lymph node biopsy to rule out lymphoma.
5. Serologic Tests: Consider serologic tests for other autoimmune conditions, such as lupus or rheumatoid arthritis.
6. Erythropoietin Level: Repeat the erythropoietin level to ensure that it is still normal, given the patient's mild anemia.
7. IGG4 Level Monitoring: Continue to monitor the patient's IgG4 levels to assess for any changes or trends.