Plantar Fasciitis: This condition is the most common cause of heel pain and is characterized by inflammation of the plantar fascia, a band of tissue that runs along the bottom of the foot. The location of pain just distal to the styloid process (which is actually a bony projection on the temporal bone, but in the context of the foot, it seems there might be a mix-up with the styloid process of the ulna or a misunderstanding of anatomical terms; however, considering the context, it likely refers to pain near the heel or the area where the plantar fascia attaches) aligns with the typical presentation of plantar fasciitis.

Heel Spur: A heel spur is a bony growth that can occur on the underside of the heel bone, often associated with plantar fasciitis. It can cause pain when walking or standing, particularly if the spur is large enough to irritate surrounding tissues.
Achilles Tendinitis: Although the Achilles tendon is located at the back of the ankle, inflammation or irritation of this tendon can sometimes refer pain to the heel area, potentially causing discomfort in the region just distal to where one might mistakenly identify a styloid process on the foot.
Fat Pad Atrophy: The fat pad under the heel can become thinner with age or due to certain conditions, leading to less cushioning and increased pressure on the heel bone, resulting in pain.

Osteomyelitis or Septic Arthritis: Infections of the bone or joint can present with localized pain and are medical emergencies. Although less common, these conditions can have severe consequences if not promptly treated.
Tumor: Both benign and malignant tumors can occur in the foot and may cause localized pain. Early detection is crucial for effective management.
Deep Vein Thrombosis (DVT): While DVT typically presents with swelling, redness, and warmth of the affected limb, pain can sometimes be the primary symptom. Given the potential for severe complications like pulmonary embolism, DVT should always be considered in the differential diagnosis of leg pain.

Tarsal Tunnel Syndrome: This is a rare condition that involves compression of the posterior tibial nerve as it travels through the tarsal tunnel on the inner side of the ankle. It can cause pain, numbness, and tingling in the foot.
Paget's Disease of Bone: A chronic condition that can result in enlarged and misshapen bones due to abnormal bone destruction and regrowth. It can cause pain in the affected bones, including those in the feet, though this is less common.