Mixed Connective Tissue Disease (MCTD): This condition is characterized by high levels of RNP antibodies and often presents with a combination of symptoms from lupus, scleroderma, and rheumatoid arthritis, making it a strong candidate given the laboratory findings.

Systemic Lupus Erythematosus (SLE): High ANA levels are a hallmark of SLE, and while RNP can be elevated, the presence of both suggests a possible diagnosis of SLE, especially if other criteria are met.
Sjögren's Syndrome: This autoimmune disorder can present with high ANA and RNP levels, particularly in cases where there's an overlap with other connective tissue diseases.
Rheumatoid Arthritis (RA): Though less common, some patients with RA can have high RNP and ANA levels, especially those with more systemic or severe disease.

Scleroderma (Systemic Sclerosis): While not as common, certain forms of scleroderma can present with high RNP and ANA levels. Missing this diagnosis could lead to delayed treatment of a potentially severe disease.
Polymyositis/Dermatomyositis: These inflammatory myopathies can occasionally have high autoantibody levels, including ANA and RNP, and are important to consider due to their significant impact on muscle function and potential for malignancy association.

Overlap Syndromes: Besides MCTD, other overlap syndromes (e.g., lupus-scleroderma overlap) can present with these autoantibody profiles but are less common.
Undifferentiated Connective Tissue Disease (UCTD): Patients may not fully meet criteria for a specific connective tissue disease but still have significant autoantibody elevations, including ANA and RNP, indicating an autoimmune process that may evolve into a defined disease over time.