Neurologic Diseases: Foot Drop

What is this condition?

Foot drop is generally a clinical manifestation of a disease of the nervous system. A neurologist is the medical specialist commonly involved in the care of these patients, and for more details of this condition please read below.

Anatomical (structural) aspects of dropping of the foot

Foot-drop occurs when there is weakness of certain muscles that help in moving the foot upwards at the ankle joint and they are called as dorsiflexor muscles of the foot. As already pointed the dorsiflexor muscles move the foot in an upward direction and the plantar flexor muscles are the foot muscles that help in its movement downwards at the ankle joint.

See that these muscles that cause dropping of foot are located above the foot level rather than within the foot itself (between the knee joint and ankle). Weakness of muscles within the foot area will not cause foot-drop.

The nerve that supplies these dorsiflexors of the foot is called as common peroneal nerve or sometimes simply as peroneal nerve. This is a branch of a larger nerve called as sciatic nerve that originates from the lumbosacral plexus. The spinal nerve roots concerned with these muscles are L4, L5 mostly. The peroneal nerve divides into superficial & deep branches. The deep branch supplies muscles of the anterior compartment of the lower leg like tibialis anterior, the muscle most frequently associated with foot-drop.

What Pathological conditions are responsible for foot-drop?

The injury or pathology of one or more of the following structures can cause foot drop;

• L4 and/or L5 spinal root
• Lumbosacral plexus
• Sciatic nerve
• Common peroneal nerve
• Deep peroneal nerve
• Muscles like tibialis anterior

At the L4 or L5 root level conditions like herniated disc, osteoarthritis, bone spurs, tumors neural foraminal stenosis, inflammation of nerve roots are responsible for this.

At a lower level, related to the other structures mentioned above, conditions like growths (tumors), traumas, infections, inflammatory conditions can cause this condition. A nerve pathology is called as neuropathy.

At the muscle level myopathy conditions (pathology within the muscle itself) can cause muscle weakness and foot-drop e.g. certain muscular dystrophies or inflammatory myopathies.

How does the patient present?

Patients characteristically present with difficulty in raising the foot above the ground. When they attempt to do so the front part of the foot lags behind so patient has to lift their legs generally higher than the normal. Also when they bring their legs down the front part of foot hits the ground first Patients will have obvious difficulty with walking due to all these.

There may be wasting or thinning of the muscles in the anterior compartment of the leg. Muscle twitching (fasciculation) may be seen. Depending upon what precipitate a foot-drop there may be additional symptoms or signs e.g. if the pathology is at the spinal root level (L4 and/or L5) then lower back pain, radiculopathy symptoms (back pain radiating down to the leg).

Patients with foot drop may also experience numbness and tingling (pins & needles) sensation in the foot and leg. There may be additional manifestations like bowel and/or bladder disturbances depending upon where is the pathology. Conditions like leprosy or vasculitis that can affect common peroneal nerve will manifest with characteristic clinical presentation (skin rashes, joint pain – vasculitis; skin patch with decreased sensation-leprosy).

Diagnosis

As above there are an abundant number of conditions that are associated with a foot-drop so varieties of neurology tests may be necessary to clinch the diagnosis. Tests are ordered on case to case basis and the following tests may be necessary;

• X-ray, CT or MRI of spine
• EMG/NCS (electromyography & nerve conduction study) of the leg
• Blood tests like ESR, ANA, B12, RPR, CPK etc
• Rarely CT or MRI of brain
• Rarely nerve and or muscle biopsy
• Rarely genetic tests etc.

Treatment

The treatment of foot drop would depend upon what caused it. Not all such conditions have a curative treatment so most of the times it is just supportive and symptomatic treatment. An ankle brace may help to keep the foot in proper position and help with ambulation better. If a herniated disc is causing this condition it may require surgery (if conservative approach fails). If peripheral neuropathy has caused it then the neuropathy is treated (e.g. diabetes management, treating vasculitis etc) and the same applies to myopathic conditions as well. Physical therapy is employed as required.

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