Differential Diagnosis
- Single most likely diagnosis
- Smoldering Myeloma or High-Risk Monoclonal Gammopathy of Undetermined Significance (MGUS): The presence of monoclonal plasma cells, a sharply abnormal free light chain (FLC) ratio, and the patient's symptoms such as recurrent boils, rash, and body pain, along with the laboratory findings, point towards a plasma cell disorder. The decision to differentiate between smoldering myeloma and high-risk MGUS requires further evaluation, including a PET/CT whole body scan and possibly a bone marrow biopsy to assess for plasma cell lesions and percentage of plasma cells.
- Other Likely diagnoses
- Systemic Lupus Erythematosus (SLE): The patient's symptoms of rash, body pain, and ulcers, along with laboratory findings of scattered interstitial T-cells and B-cells, could suggest an autoimmune disorder like SLE. However, the presence of monoclonal plasma cells and the specific FLC ratio abnormality are not typical for SLE.
- Vasculitis: The description of the patient's rash and ulcers, along with the body pain and flank pain, could be indicative of a vasculitic process. However, the monoclonal plasma cell finding and the specific immunophenotypic markers would need to be correlated with clinical and morphologic findings.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Multiple Myeloma: Although the bone marrow biopsy showed less than 10% plasma cells, the presence of monoclonal plasma cells, abnormal FLC ratio, and the patient's clinical presentation necessitate ruling out multiple myeloma, especially given the potential for plasma cell lesions on imaging.
- Infectious Diseases (e.g., Endocarditis, Osteomyelitis): The recurrent boils and ulcers could be indicative of an underlying infectious process, which, if not properly treated, could lead to severe complications.
- Rare diagnoses
- POEMS Syndrome: This rare disorder is characterized by polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy, and skin changes. The patient's symptoms of body pain, rash, and the presence of monoclonal plasma cells could suggest POEMS syndrome, although this would be less likely without additional specific findings such as polyneuropathy.
- Castleman Disease: This rare lymphoproliferative disorder can present with a variety of systemic symptoms, including rash, body pain, and lymphadenopathy, along with laboratory abnormalities. However, the specific findings of monoclonal plasma cells and the sharply abnormal FLC ratio would need careful correlation with clinical and morphologic features.