Erfan Bashar
Back to Neuropathies

Neuropathies — Diabetic Neuropathy

~3 min read
Last medically reviewed:
On this pageTable of contents

Educational scope notice: This is a study note for medical students, not medical advice, diagnosis, or treatment guidance. Clinical management should follow local protocols and current guidelines.

Diabetes is the single most common cause of polyneuropathy, but diabetic neuropathy is not one disease. It is a group of disorders sharing a metabolic trigger, and each pattern carries different implications for management and prognosis.

Patterns at a glance

Focal and multifocal forms include cranial mononeuritis (typically pupil-sparing third or sixth nerve palsy), thoracic or abdominal radiculopathy, single-limb neuropathies such as femoral involvement, carpal tunnel syndrome (more frequent in diabetes), and the painful proximal syndrome described below.

Diffuse symmetric forms include distal chronic sensorimotor polyneuropathy (DSPN, the most common), small-fibre neuropathy, large-fibre neuropathy, and autonomic neuropathy. Subclinical disease detectable only on conduction studies sits beneath all of these.

How diabetes injures nerves

Four pathways contribute. Chronic hyperglycemia drives sorbitol accumulation and oxidative stress in the small vessels supplying nerves, which is the main engine of DSPN: the longest nerves suffer first because they depend on the longest nutritive arteries. Immune-mediated microvasculitis with perivascular inflammation drives the proximal painful syndrome instead. Metabolic swelling makes nerves more vulnerable to compression, which is one reason carpal tunnel syndrome clusters in diabetes. Small-vessel infarcts cause abrupt focal palsies such as cranial nerve lesions. Rapid tightening of glycemic control can also transiently worsen pain, so new or flaring symptoms after intensified treatment have their own explanation.

Distal symmetric polyneuropathy

DSPN is the most common diabetic neuropathy. Onset is slow, chronic, and length-dependent, beginning in the feet. Sensory complaints include numbness, tingling, burning, deep aching pain worse at night, and stabbing pains, sometimes with allodynia. Motor involvement is slight and distal; a predominantly motor picture in a diabetic patient should prompt a search for another cause. Proprioceptive loss can produce sensory ataxia, and ankle reflexes fade.

The defining danger is painlessness. When the fibres that should report injury are dead, wounds go unnoticed: the classic story is a foot ulcer with osteomyelitis in a patient who never felt the original cut. DSPN does not reverse with treatment. Management aims to slow progression through glycemic, blood pressure, lipid, and smoking control, protect insensate feet, and treat pain, as covered under treatment (/notes/neurology/neuropathies-treatment/).

Diabetic lumbosacral radiculoplexoneuropathy

DLRPN differs markedly from DSPN. It presents with severe unilateral thigh pain that burns, worsens at night, and stays constant regardless of position, unlike radicular pain, which shifts with posture. Proximal weakness of quadriceps and hip flexors follows, with marked wasting, weight loss, and an absent knee jerk. Thoracic and cervical variants exist but the lumbar form dominates.

The mechanism is immune-mediated microvasculitis rather than metabolic injury, which explains two properties that distinguish it from DSPN: it often affects patients with recently diagnosed or well-controlled diabetes rather than long-standing hyperglycemia, and immunotherapy is sometimes discussed, though pain control and physiotherapy remain central regardless. The course is generally favorable over 6 to 18 months. EMG shows denervation in proximal muscles and spinal fluid protein is often raised, reflecting inflammation.

Small-fibre and autonomic patterns

Diabetes is the most common cause of small-fibre neuropathy: burning, stabbing distal pain with preserved reflexes and strength, confirmed by skin biopsy when needed. Autonomic neuropathy brings orthostatic hypotension, post-meal fullness and gastroparesis, erectile dysfunction, urinary retention, and reduced sweating. It marks advanced disease and substantially raises mortality risk, so its presence changes the seriousness of the overall assessment.

Evidence anchors

Suggest a correction