Morton's neuroma: Although an ultrasound did not show a neuroma, clinical presentation is highly suggestive, and ultrasound may not always detect neuromas. The description of pain like walking on golf balls is classic for Morton's neuroma.

Metatarsalgia: This condition involves pain and inflammation in the ball of the foot, which could be due to various factors including poor foot mechanics, overuse, or footwear issues. The symptoms can mimic those of a neuroma.
Sesamoiditis: Inflammation of the sesamoid bones or the tendons surrounding them can cause pain in the forefoot, similar to walking on golf balls.
Plantar plate tear: A tear in the plantar plate, which is a ligament that supports the toes, can cause forefoot pain and could be considered given the symptom description.

Osteoid osteoma: A benign bone tumor that can cause severe pain, often worse at night and relieved by NSAIDs. Although rare, missing this diagnosis could lead to prolonged pain and disability.
Bone infection (osteomyelitis): Infection of the bone can cause severe pain and is a medical emergency. It's crucial to consider this, especially if there's a history of trauma, recent travel, or immune compromise.
Tumor (e.g., Ewing's sarcoma): Although extremely rare, a tumor in the foot could cause the described symptoms. Missing such a diagnosis could have severe consequences.

Freiberg's disease: A rare condition that affects the metatarsal bones, causing pain and stiffness in the forefoot. It's more common in adolescents but can occur in adults.
Kohler's disease: A rare bone disorder causing pain and swelling in the foot, typically affecting children but can be considered in adults with atypical presentations.
Gout or pseudogout: Although more commonly associated with the big toe, these conditions can cause sudden, severe pain in other parts of the foot, including the forefoot.