Repetitive Strain Injury or Overuse Syndrome: This is a common condition in young adults, especially if they have recently increased their physical activity or have jobs that involve repetitive movements. The lack of swelling and erythema (redness) suggests a non-inflammatory cause, and the distribution of pain could be related to specific activities or postures.

Early Rheumatoid Arthritis (RA): Although RA typically presents with symmetric joint involvement, early stages can be asymmetric. The absence of swelling and erythema does not rule out RA, as these symptoms can be minimal in the early stages.
Gout: Gout can present with acute, severe pain in one joint (monoarthritis), but it can also affect multiple joints. The right middle finger could be a target for a gouty attack, and ankles are common sites as well. However, gout usually presents with significant swelling and erythema, which is not mentioned here.
Psoriatic Arthritis: This condition can cause joint pain and inflammation, similar to RA, but it is often associated with psoriasis. The pattern of joint involvement can be asymmetric, and it might not always include significant swelling or erythema in the early stages.

Osteonecrosis (Avascular Necrosis): This condition, which involves the death of bone tissue due to a lack of blood supply, can cause pain in the affected joints without significant swelling or erythema. It's crucial to consider this diagnosis, especially if the patient has risk factors such as steroid use or significant trauma.
Infectious Arthritis: Although less likely given the absence of significant swelling or erythema, infectious arthritis (septic arthritis) is a medical emergency that requires prompt diagnosis and treatment. It can present with pain and limited range of motion, even in the absence of overt signs of infection.
Lyme Disease: Caused by the bacterium Borrelia burgdorferi, Lyme disease can lead to arthritis, typically affecting the knees but potentially other joints as well. Early stages might not include the characteristic "bull's-eye" rash or significant swelling.

Sarcoidosis: A systemic disease that can cause arthritis among other symptoms. Joint involvement in sarcoidosis can be variable and might not always include significant inflammation.
Hemochromatosis: A genetic disorder leading to iron overload, which can cause arthritis, typically in the second and third metacarpophalangeal joints but potentially in other joints as well, including ankles.
Relapsing Polychondritis: A rare autoimmune disorder that can cause cartilage inflammation, leading to joint pain and other symptoms. It's less likely given the specific pattern of joint involvement but should be considered in the differential diagnosis of unexplained joint pain.