Overuse or Repetitive Strain Injury: This is the most likely diagnosis due to the common occurrence of repetitive strain injuries in the forearms, especially in individuals who perform repetitive tasks with their hands and wrists, such as computer users, athletes, or laborers. The bilateral nature of the pain suggests a systemic or repetitive cause rather than a localized injury.

Tennis Elbow (Lateral Epicondylitis): Although typically unilateral, if both arms are involved in similar activities, it's possible for tennis elbow to cause bilateral pain. The pain is usually on the lateral (outer) aspect of the elbow but can radiate down the forearm.
Medial Epicondylitis (Golfer's Elbow): Similar to tennis elbow, this condition affects the medial (inner) aspect of the elbow and can cause pain that radiates down the forearm. Bilateral involvement is less common but possible, especially in individuals who use both arms symmetrically.
Radial Nerve Compression: Compression of the radial nerve can cause pain, weakness, and numbness in the back of the hand or the thumb side of the hand and forearm. If both arms are affected, it could lead to bilateral dorsal forearm pain.

Multiple Myeloma: Although rare, multiple myeloma can cause bone pain, including in the forearms, due to the proliferation of malignant plasma cells in the bone marrow. It's crucial to consider this diagnosis to avoid missing a potentially life-threatening condition.
Hypocalcemia or Hypercalcemia: Electrolyte imbalances, particularly those affecting calcium levels, can cause muscle cramps, spasms, and pain, including in the forearms. These conditions can be associated with serious underlying diseases and require prompt diagnosis and treatment.
Vasculitis: Inflammation of the blood vessels can cause a wide range of symptoms, including pain in the arms. Certain types of vasculitis, like giant cell arteritis or polyarteritis nodosa, can be severe and require immediate medical attention.

Eosinophilia-Myalgia Syndrome: A rare condition characterized by muscle pain, eosinophilia (elevated eosinophil count), and sometimes skin changes, which could potentially cause forearm pain.
Fibromyalgia: A chronic condition characterized by widespread musculoskeletal pain, fatigue, and tenderness in localized areas. While not typically causing isolated forearm pain, it could be considered in the differential diagnosis for diffuse or widespread pain patterns.
Peripheral Artery Disease (PAD): Although more commonly associated with leg pain, PAD can cause arm pain, especially if the disease is widespread or if there's significant stenosis or occlusion in the arteries supplying the arms.