Focal and multifocal neuropathy - Complications of diabetes

Focal and multifocal neuropathy

Pathophysiology

A focal nerve lesion, either of a cranial or peripheral nerve, which is thought to be due to occlusion of a larger vessel supplying the nerve, or pressure damage, when it may be seen in the context of impaired sensation of pain. Several nerves may be affected.

·        The cranial nerves most affected are III, IV and VI.

·        The peripheral nerves most affected are the median, ulnar and lateral popliteal nerves.

·        If a large nerve trunk or root is affected, such as the femoral nerve, radiculopathy results, causing proximal pain and wasting, for example in the thigh, with weakness and wasting of quadriceps (diabetic amyotrophy).

Clinical features

Any nerve(s) can be involved.

·        Third nerve palsy typically presents with pain, diplopia and ptosis. It may resolve spontaneously.

·        Peripheral nerve palsies recover only slowly and often incompletely.

·        Diabetic amyotrophy present with sudden onset of pain and weakness with an absent tendon jerk (usually the knee). The important differential diagnosis is a spinal or cauda equina cause of the radiculopathy.

Investigations

In most cases, this is not necessary, as the cause is clear. Occasionally, it may be useful to exclude other causes, particularly in cranial nerve palsies when a space-occupying lesion may be excluded with CT or MRI.

Management

Management is as for diffuse symmetrical neuropathies.