What are the differential diagnoses for a patient with persistently elevated Immunoglobulin G4 (IgG4) levels, normocytic anemia, and chronic skin lesions with extensive fibrosis and numerous fibroblasts on biopsy, unresponsive to broad-spectrum antibiotics and topical steroids, including Bactroban (mupirocin) and topical corticosteroids?

Differential Diagnosis

The patient's presentation is complex, with 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 fibrosis and fibroblasts on biopsy, and unexplained weight loss support this diagnosis.
• Other Likely Diagnoses
  • Chronic Inflammatory Disease: The patient's symptoms, such as skin sores and unexplained weight loss, could be indicative of a chronic inflammatory disease, such as rheumatoid arthritis or lupus.
  • Infectious Disease: The positive test for Filariasis AB IGG4, although unlikely given the patient's travel history, suggests an infectious etiology. Other infections, such as Lyme disease or tuberculosis, could also be considered.
  • Malignancy: The patient's unexplained weight loss and skin sores that fail to heal could be indicative of an underlying malignancy, such as lymphoma or leukemia.
• Do Not Miss Diagnoses
  • Lymphoma: A diagnosis of lymphoma would be catastrophic if missed. The patient's symptoms, such as unexplained weight loss and skin sores, could be indicative of lymphoma.
  • Sarcoidosis: Sarcoidosis is a systemic disease that can present with skin lesions, weight loss, and elevated inflammatory markers. Although the patient's biopsy results do not show granulomas, sarcoidosis is still a possible diagnosis.
  • Vasculitis: Vasculitis, such as granulomatosis with polyangiitis, could present with skin lesions, weight loss, and elevated inflammatory markers.
• Rare Diagnoses
  • Eosinophilic Fasciitis: Although the patient's CBC with differentials has never shown elevated eosinophils, eosinophilic fasciitis is a rare disease that could present with skin lesions and fibrosis.
  • Nephrogenic Systemic Fibrosis: This rare disease is characterized by fibrosis of the skin and other organs, and could be considered given the patient's biopsy results showing extensive fibrosis.
  • Scleromyxedema: This rare disease is characterized by lichenoid papules, scleroderma-like skin changes, and fibrosis, and could be considered given the patient's skin lesions and biopsy results.

Recommendations

1. Repeat skin biopsies: Consider repeat skin biopsies to rule out other diagnoses, such as lymphoma or sarcoidosis.
2. Imaging studies: Consider imaging studies, such as CT or MRI, to evaluate for underlying malignancy or other systemic diseases.
3. Infectious disease workup: Consider a more thorough infectious disease workup, including tests for Lyme disease, tuberculosis, and other infections.
4. Rheumatologic workup: Consider a rheumatologic workup, including tests for rheumatoid arthritis, lupus, and other autoimmune diseases.
5. Hematologic workup: Consider a hematologic workup, including tests for lymphoma and other blood disorders.
6. Consider referral to a specialist: Consider referral to a specialist, such as a dermatologist, rheumatologist, or hematologist, to further evaluate and manage the patient's condition.