Atypical diabetic neuropathies

Adapted from BMJ 11 October 2025

About half of all patients with diabetes will develop a symmetrical polyneuropathy but several other atypical nerve conditions can also occur.

Treatment induced neuropathy of diabetes is an acute and severely painful small fibre neuropathy that occurs with a steep drop in glycated haemoglobin levels.

Radiculoplexus neuropathies include lumbosacral, cervical, and thoracic forms, in which pain and weight loss are followed by weakness and sensory loss in the distribution of a single anatomical region.

Monophasic cranial neuropathies are caused by non-inflammatory microvascular ischaemia and present acutely followed by slow improvement.

Compressive neuropathies are when nerves are compressed.

There is more chronic inflammatory demyelinating polyneuropathy in patients with diabetes than in the general population, but definitive diagnosis is difficult to ascertain when diabetes is also present.

Diabetes now affects 9.3% of the world’s population, and half of them have typical symmetric neuropathy. Carpal tunnel syndrome affects 20-30% of diabetics. Cranial neuropathies affect 1% of the population which is ten times higher than in the general population. Over a five year period, about 10% of diabetics will get a treatment induced neuropathy. Lumbosacral neuropathy will eventually affect 1% of diabetics. Chronic inflammatory demyelinating neuropathy affects 0.7 to 10.3 people for every 100,000 people. It is the rarest type.

Treatment induced neuropathy is associated with a high rate of damage to the retina and kidney. It is thought that neuronal ischaemia and the release of cytokines damage the small blood vessels to the nerves.

Prior high blood glucose is the main risk factor for this type of neuropathy. Pain, and autonomic symptoms occur such as low blood pressure, gut dysmotility and sexual dysfunction. The usual age of onset is 25 in type one diabetes and 51 in type two diabetes. The faster the rate in improvement in blood sugars, the higher the risk.

The usual presenting problem is pain in the arm or leg within six to eight weeks of rapid blood sugar correction. The pain is usually in the glove and stocking distribution. Unfortunately the pain is often difficult to treat even with modern drugs such as tricyclic antidepressants, SSRIs, gabapentinoids, and sodium channel blockers. The condition and pain usually stablise over three years if the blood sugars can be kept in control and stable. Foot ulceration can become a common problem if the condition becomes recurrent due to blood sugar swings.

Radiculoplexus neuropathy is caused by a vasculitis of affected nerve roots, plexus and individual nerves in the back. Most people have pain. Rapid glycaemic control can be a pre-disposing factor. Leg weakness, foot drop, numbness and autonomic symptoms can occur. It usually stays one sided.

Post surgical inflammatory neuropathy is typically defined as a neuropathy occurring within 30 days of a surgical event. It occurs in non diabetics too, but more often in diabetics.

Multiple mononeuropathies can also occur in diabetics. This tends to affect the lower arm or lower leg.

Figuring out what type of neuropathy is occurring may be done on clinical history and examination, electrodiagnostic testing, MRI scans, blood tests, lumbar puncture, and nerve biopsy.

Most neuropathies require good blood sugar control to improve, may worsen for a period of time before improvement, and may need drug or other treatments and supportive aids such as braces and wheelchairs. Sometimes residual motor deficits such as foot drop can persist long term.

For Facial mononeuropathy a short course of oral steroids starting within 72 hours of onset may improve recovery.

GLP-1 based treatment for diabetes, weight control, and fatty liver disease is rapidly increasing. These agents also rapidly reduce HbA1c levels. A study was done to specifically look at the effects on type two diabetics and polyneuropathy risk on these agents. One group got the weight loss injection and the other got metformin and insulin. Over five years there was no difference in neuropathy diagnoses.