Ulnar Nerve Entrapment or Neuropathy: This condition often presents with pain and paresthesia in the distribution of the ulnar nerve, which typically affects the 4th and 5th fingers. The involvement of the 3rd finger could be due to variations in nerve distribution or the presence of a more proximal lesion affecting multiple nerves.

Carpal Tunnel Syndrome: Although carpal tunnel syndrome primarily affects the median nerve, which typically supplies the 1st, 2nd, and 3rd fingers, some patients may experience symptoms in the ulnar distribution due to the anatomical variability or a more extensive neuropathic process.
Tendinitis or Tenosynovitis of the Fingers: Inflammation of the tendons or their sheaths in the fingers can cause pain on motion, especially if the tendons of the 3rd, 4th, and 5th fingers are involved.
Osteoarthritis or Rheumatoid Arthritis: These conditions can cause pain in the fingers, especially with movement, due to joint inflammation and degeneration.

Acute Compartment Syndrome: A medical emergency that requires prompt diagnosis and treatment. It can cause severe pain, especially on passive stretching of the muscles within the compartment, and can lead to permanent damage if not addressed promptly.
Infections (e.g., Cellulitis, Abscess): Infections in the hand can cause severe pain, swelling, and limited mobility. Early recognition and treatment are crucial to prevent serious complications.
Ganglion Cysts: Although typically not painful unless they compress a nerve, large ganglion cysts can cause significant discomfort and should be considered in the differential diagnosis.

Sarcoidosis: A systemic disease that can cause inflammation in various parts of the body, including the hands, leading to pain and stiffness.
Gout or Pseudogout: These conditions can cause acute, severe pain in the fingers due to crystal deposition in the joints.
Erythromelalgia: A rare disorder characterized by burning pain, heat, and redness in the hands and feet, which can be exacerbated by movement.