Osteoarthritis (OA): Given the patient's age and the presence of widespread joint pain, OA is a common condition that affects multiple joints and is more prevalent with increasing age. The absence of significant inflammatory markers (CRP negative, mildly elevated ESR) and low rheumatoid factor levels, especially the IgM component, also points towards a non-inflammatory cause like OA.

Seronegative Rheumatoid Arthritis: Although the rheumatoid factor is not significantly elevated, some patients with rheumatoid arthritis (RA) can be seronegative. The presence of widespread joint pain and a slightly elevated ESR could still suggest RA, especially if there are other clinical features such as morning stiffness, symmetric joint involvement, and specific joint patterns.
Fibromyalgia: Characterized by widespread musculoskeletal pain accompanied by fatigue, sleep, memory, and mood issues. The absence of significant inflammatory markers and the presence of widespread pain without a clear inflammatory or structural cause could suggest fibromyalgia.
Psoriatic Arthritis: Especially if the patient has psoriasis or a history of psoriasis. The presence of joint pain and a mild elevation in ESR could be consistent with psoriatic arthritis, although typically, this condition would have more significant inflammatory markers or skin manifestations.

Lyme Arthritis: Caused by Borrelia burgdorferi, transmitted by tick bites. It can cause intermittent or persistent arthritis, primarily in large joints. Although less likely without specific exposure history or other symptoms like erythema migrans, it's crucial to consider due to its potential for serious complications if untreated.
Septic Arthritis: An infection within a joint, which is a medical emergency. Even though the patient's inflammatory markers are not significantly elevated, septic arthritis can present with variable degrees of inflammation, and missing this diagnosis could lead to severe joint damage or systemic infection.
Multiple Myeloma: A plasma cell dyscrasia that can cause widespread bone pain and elevated ESR. Although less common, it's a critical diagnosis not to miss due to its significant implications for treatment and prognosis.

Relapsing Polychondritis: A rare autoimmune disorder characterized by recurrent episodes of cartilaginous inflammation. It could present with joint pain among other symptoms like auricular or nasal chondritis.
Sjögren's Syndrome: An autoimmune disorder that can cause widespread joint pain, among other symptoms like dry eyes and dry mouth. It might be considered if there are other systemic symptoms or specific autoantibodies.
Adult-Onset Still's Disease: A rare inflammatory disorder that can cause widespread joint pain, fever, and rash. Although it's rare, it should be considered in the differential diagnosis of widespread joint pain with inflammatory features.