Differential Diagnosis for Polyarthralgia with Mildly Elevated Complement 4
- Single most likely diagnosis:
- Fibromyalgia: This condition is characterized by widespread musculoskeletal pain and is often associated with polyarthralgia. The absence of positive labs for autoimmune diseases and the mild elevation of complement 4, which is not specific, supports this diagnosis.
- Other Likely diagnoses:
- Osteoarthritis: Although it typically presents with more localized joint pain, osteoarthritis can cause polyarthralgia, especially in older adults. The lack of systemic symptoms and negative autoimmune labs make this a plausible diagnosis.
- Menstrual or hormonal-related arthralgias: Hormonal fluctuations can cause joint pain in some women. Given the patient's gender and the absence of other systemic symptoms or positive autoimmune labs, this could be a contributing factor.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.):
- Parvovirus B19 infection: Although less common, parvovirus B19 can cause polyarthralgia and has been associated with mild elevations in complement levels. It's crucial to consider infectious causes, especially if the patient has been exposed to others with similar symptoms.
- Hematologic malignancies (e.g., lymphoma): Some malignancies can present with polyarthralgia and mildly elevated complement levels. A thorough history, physical examination, and possibly additional labs (e.g., blood cell counts, serum protein electrophoresis) are necessary to rule out these conditions.
- Rare diagnoses:
- Relapsing polychondritis: This rare autoimmune disorder can cause polyarthralgia among other symptoms like cartilage inflammation. The negative labs for common autoimmune diseases do not entirely rule out this condition, but it is less likely.
- Mixed Connective Tissue Disease (MCTD): Although the patient has negative labs for lupus, Sjögrens, and RA, MCTD can sometimes present with polyarthralgia and have negative or borderline autoimmune labs. It's a diagnosis of exclusion and might require further evaluation over time.