Thoracic Outlet Syndrome (TOS): This condition involves compression of the nerves and/or blood vessels that pass into the thoracic outlet (the space between your collarbone and first rib). It can cause symptoms like hand cramping, especially if the compression affects the nerves. The presence of a large wrist fistula might indirectly suggest altered anatomy or increased pressure in the region that could exacerbate TOS symptoms.

Carpal Tunnel Syndrome: Although typically associated with median nerve compression at the wrist, it can cause cramping and locking sensations in the hand. The symptoms could be exacerbated or mimicked by the altered anatomy or pressure dynamics due to the wrist fistula.
Ulnar Nerve Compression: Compression of the ulnar nerve at the elbow or wrist can lead to hand cramping and weakness, particularly in the fingers innervated by this nerve.
Vascular Steal Syndrome: In the context of a fistula, especially an arteriovenous fistula, there can be a diversion of blood flow that might lead to ischemic symptoms in the hand, including cramping, despite good overall perfusion.

Compartment Syndrome: Although less likely given the good perfusion, compartment syndrome is a medical emergency that requires prompt intervention. It involves increased pressure within a muscle compartment that can lead to nerve and muscle damage.
Ischemic Monomelic Neuropathy: A condition that can occur in the setting of vascular access procedures or fistulas, leading to nerve damage due to ischemia.

Hematoma or Pseudotumor: Rare complications of fistulas that could potentially compress nerves or vessels, leading to cramping.
Nerve Tumors: Such as schwannomas or neurofibromas, which could compress nerves and cause symptoms like hand cramping.
Amyloidosis: A condition characterized by the deposition of amyloid proteins in various tissues, including nerves, which could lead to neuropathy and symptoms like hand cramping, although this would be a very rare and indirect cause.