Differential Diagnosis for Left Ankle Dorsiflexor Weakness

Single Most Likely Diagnosis

• Peroneal nerve injury or compression: This is a common complication after back surgery, especially if the patient was in a prone position for an extended period. The peroneal nerve can be compressed or injured, leading to weakness in the muscles it innervates, including the dorsiflexors of the foot.

Other Likely Diagnoses

• Radiculopathy (L5 nerve root): Although the EMG/NCV test was normal, it's essential to consider radiculopathy, especially if the back surgery involved the lumbar spine. The L5 nerve root is responsible for controlling the muscles involved in ankle dorsiflexion.
• Neuropathy (small or intermediate fiber): Some neuropathies, such as those caused by diabetes or vitamin deficiencies, can affect small or intermediate fibers, which may not be detected on standard EMG/NCV tests. However, these conditions would typically have other associated symptoms and signs.
• Local muscle or tendon injury: Direct injury to the muscles or tendons responsible for ankle dorsiflexion during surgery or post-operative period could lead to weakness.

Do Not Miss Diagnoses

• Cauda equina syndrome: Although less likely, cauda equina syndrome is a serious condition that can occur after back surgery, causing nerve root compression and potentially leading to significant neurological deficits, including weakness, numbness, and bladder/bowel dysfunction.
• Spinal epidural hematoma or abscess: These conditions can cause compression of the spinal cord or nerve roots, leading to neurological deficits, including weakness. Prompt diagnosis and treatment are crucial to prevent long-term damage.

Rare Diagnoses

• Amyotrophic lateral sclerosis (ALS): A rare and progressive neurological disease that can cause muscle weakness, including ankle dorsiflexor weakness. However, ALS would typically have other associated symptoms and signs, such as widespread muscle weakness, atrophy, and fasciculations.
• Charcot-Marie-Tooth disease: A group of inherited disorders that affect the peripheral nerves, leading to muscle weakness and atrophy. However, this condition would typically have a long-standing history of symptoms and signs, rather than an acute onset after surgery.
• Small fiber neuropathy: A condition that affects the small nerve fibers, which can cause pain, numbness, and autonomic dysfunction. While it may not be detected on standard EMG/NCV tests, it would typically have other associated symptoms and signs, such as burning pain or autonomic dysfunction.