Neurology · PANCE / PANRE

Diabetic Peripheral Neuropathy

Most common complication of diabetes; distal symmetric stocking-glove sensorimotor neuropathy.

Also known as: diabetic neuropathy, diabetic peripheral neuropathy, DPN, distal symmetric polyneuropathy, DSPN

Overview

Distal symmetric, length-dependent, predominantly sensory polyneuropathy that develops as a complication of long-standing diabetes mellitus, after exclusion of other causes. Encompasses several syndromes; distal symmetric polyneuropathy (DSPN) is the most common form.

Epidemiology

Prevalence ~30-50% of patients with diabetes (rises with disease duration); ~10-20% have painful diabetic neuropathy. The most common cause of peripheral neuropathy in the US. Leading cause of non-traumatic lower-extremity amputation.

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Risk factors

Duration of diabetes
Poor glycemic control (higher A1c)
Older age
Hypertension, dyslipidemia (especially elevated triglycerides), obesity
Smoking and alcohol use
Type 1 diabetes (autoimmune component) and type 2 diabetes
Tall stature (longer axons)
Vitamin B12 deficiency (often comorbid; metformin exacerbates)
Genetic susceptibility

Pathophysiology

Multifactorial: chronic hyperglycemia leads to polyol pathway flux (sorbitol accumulation), advanced glycation end-product (AGE) formation, oxidative stress, protein kinase C activation, mitochondrial dysfunction, and microvascular insufficiency of the vasa nervorum. Length-dependent dying-back axonopathy preferentially affects long, small-fiber (unmyelinated C, thinly myelinated Aδ) sensory and autonomic axons first, then larger myelinated fibers; longest axons (toes, feet) are affected first.

Clinical presentation

Symptoms

Insidious onset, stocking-then-glove progression
Sensory: numbness, tingling, burning, prickling, allodynia (pain from non-painful stimuli), hyperalgesia, lancinating pain
Symptoms often worse at night
Loss of protective sensation predisposes to unnoticed foot injury, ulceration, and Charcot arthropathy
Motor: weakness late (intrinsic foot, then distal lower-extremity), foot drop occasional
Autonomic: orthostatic hypotension, resting tachycardia, gastroparesis, neurogenic bladder, erectile dysfunction, gustatory sweating, anhidrosis of feet (predisposes to dry, cracked skin)
Atypical syndromes: diabetic amyotrophy (proximal asymmetric leg weakness with pain), cranial mononeuropathies (CN III with pupil sparing, CN VI), thoracic radiculoneuropathy, treatment-induced neuropathy after rapid glucose lowering

Signs / physical exam

Stocking-distribution decreased pinprick, light touch, vibration (128-Hz tuning fork), and proprioception
Diminished or absent ankle reflexes (knee reflexes usually preserved early)
10-g Semmes-Weinstein monofilament insensate at one or more sites — high sensitivity for risk of foot ulceration
Intrinsic foot muscle wasting, hammer/claw toes, pes cavus deformity (late)
Romberg may be positive (large-fiber involvement)
Look for foot ulcers, fissures, calluses, Charcot deformity
Autonomic: postural BP drop, resting tachycardia, abnormal heart rate variability

Classic findings

Symmetric stocking-distribution sensory loss with absent ankle reflexes in a patient with diabetes.

Differential diagnosis

Vitamin B12 deficiency — Sensory ataxia (loss of proprioception, positive Romberg), macrocytic anemia, cognitive changes; check B12, MMA, homocysteine; often coexists with DPN, especially on metformin
Alcohol-related neuropathy — History of heavy alcohol use, nutritional deficiencies (thiamine, B6, folate)
Chemotherapy-induced peripheral neuropathy — Platinums, taxanes, vincristine, bortezomib; temporal relation to chemotherapy
Hypothyroidism — Cold intolerance, weight gain, constipation, dry skin; elevated TSH
Chronic kidney disease (uremic neuropathy) — Advanced renal failure; improves with dialysis or transplant
Monoclonal gammopathy / amyloidosis — SPEP/UPEP, immunofixation, free light chains; check in older patients with rapidly progressive or painful neuropathy
Vasculitis (mononeuritis multiplex) — Multifocal, asymmetric, often painful; constitutional symptoms; nerve biopsy if needed
Chronic inflammatory demyelinating polyneuropathy (CIDP) — Symmetric proximal AND distal weakness, areflexia, elevated CSF protein; treat with IVIG, steroids, plasma exchange — distinct from DPN and IMPORTANT not to miss
Hereditary neuropathy (Charcot-Marie-Tooth) — Family history, foot deformity (pes cavus, hammer toes), early onset
Heavy metal toxicity (lead, arsenic, mercury), HIV, hepatitis C, Lyme disease, paraneoplastic — History clues, targeted serology and toxicology

Diagnostic workup

Diagnostic criteria

ADA/Toronto Consensus: typical DPN = patient with diabetes and distal symmetric polyneuropathy attributable to diabetes after exclusion of other causes; supported by characteristic signs/symptoms and confirmed by nerve conduction studies (in atypical or research settings).

Labs

Confirm diabetes and assess control: fasting glucose, A1c
Exclude common alternative or coexisting causes: CBC, BMP, TSH, vitamin B12 (with MMA if borderline), serum/urine protein electrophoresis with immunofixation (especially in older patients or atypical features), LFTs
Consider HIV, hepatitis C, Lyme, heavy metals, paraneoplastic antibodies if clinical suspicion
Lipid panel (cardiovascular risk and triglyceride-related neuropathy)

Imaging

Electrodiagnostic studies (NCS/EMG): not routinely required for typical DPN, but indicated for atypical features (asymmetric, predominantly motor, rapidly progressive, proximal involvement, areflexia, family history) to distinguish from CIDP, hereditary, or compressive neuropathies
Foot exam with monofilament and tuning fork at least annually in all patients with diabetes (ADA/IWGDF recommendation)
Skin biopsy for intraepidermal nerve fiber density and corneal confocal microscopy — research/specialty tools for small-fiber neuropathy

Diagnostic algorithm

Drug Class	Examples	Common Adverse Effects	Notes
Gabapentinoid	Pregabalin, gabapentin	Sedation, dizziness, edema, weight gain	Pregabalin FDA-approved; renal dose adjustment
SNRI	Duloxetine, venlafaxine	Nausea, dry mouth, somnolence, BP rise	Duloxetine FDA-approved; caution with hepatic disease
TCA	Amitriptyline, nortriptyline	Anticholinergic, QT prolongation, orthostasis	Avoid in elderly and cardiac disease; nortriptyline better tolerated
Opioid (atypical)	Tapentadol ER, tramadol	Sedation, constipation, dependence, serotonin syndrome (tramadol + SNRI/SSRI)	Tapentadol FDA-approved; opioids generally avoided long-term
Topical	Capsaicin 8% patch, lidocaine 5%	Local burning, erythema (capsaicin)	Capsaicin 8% FDA-approved; in-office application
Neuromodulation	10-kHz spinal cord stimulation	Procedural risks, lead migration	FDA-approved 2021 for refractory painful DPN

Pharmacologic and neuromodulatory options for painful diabetic peripheral neuropathy.

Treatment

First-line

Glycemic control — strongest evidence for delaying progression in type 1 (DCCT/EDIC); more modest effect in type 2 (UKPDS, ACCORD). Avoid hypoglycemia in autonomic neuropathy.
Cardiovascular risk factor management: BP control (<130/80), statin therapy, smoking cessation, weight loss
Foot care education: daily inspection, well-fitting footwear, no barefoot walking, podiatry care; annual comprehensive foot exam by clinician; offload pressure points
Symptomatic treatment of painful DPN — FDA-approved or first-line agents (ADA 2022, AAN):
• Pregabalin 150-600 mg/day in divided doses (FDA-approved; sedation, edema, weight gain)
• Duloxetine 60-120 mg/day (FDA-approved; nausea, dry mouth, somnolence, hepatic caution)
• Gabapentin 900-3600 mg/day in divided doses (off-label but widely used; sedation, dizziness, edema)
• Tricyclic antidepressant — amitriptyline, nortriptyline 25-100 mg qhs (anticholinergic side effects, QT prolongation, orthostasis — caution in elderly and cardiac disease)
• Tapentadol ER (FDA-approved) — opioid; consider only after non-opioid options exhausted
Topical agents: capsaicin 8% patch (FDA-approved), topical lidocaine 5%

Second-line / adjunct

Combination therapy if monotherapy insufficient (e.g., gabapentinoid + duloxetine, gabapentinoid + TCA)
Tramadol short-term; avoid chronic opioids if possible (limited efficacy, dependence/overdose risk)
Spinal cord stimulation (10-kHz high-frequency) — refractory painful DPN; FDA-approved 2021
Treat autonomic complications: orthostatic hypotension (compression stockings, midodrine, droxidopa, fludrocortisone), gastroparesis (small frequent meals, metoclopramide — limit duration; prokinetics; gastric pacing), neurogenic bladder (timed voiding, intermittent catheterization), erectile dysfunction (PDE5 inhibitors)
Address vitamin B12 deficiency (oral 1000 mcg/day or parenteral); ADA recommends periodic B12 screening in patients on chronic metformin
Aldose reductase inhibitors and alpha-lipoic acid — modest evidence; not FDA-approved in the US
Multidisciplinary diabetes care including podiatry, vascular surgery, and wound care for at-risk feet
Smoking cessation counseling, alcohol reduction

Complications

Foot ulceration and infection
Charcot neuroarthropathy (painless midfoot collapse with bony destruction; needs prompt offloading and immobilization)
Lower-extremity amputation (DPN is the leading cause of non-traumatic amputation)
Falls and fractures from sensory ataxia and proprioceptive loss
Cardiovascular autonomic neuropathy → silent ischemia, sudden cardiac death, exercise intolerance
Gastroparesis with poor glycemic control, weight loss, bezoar formation, esophagitis
Neurogenic bladder → UTIs, urinary retention
Erectile dysfunction and orgasmic dysfunction
Hypoglycemia unawareness from autonomic failure
Chronic pain → depression, sleep disturbance, opioid dependence

PANCE pearls

Always exclude other causes of neuropathy before attributing all symptoms to diabetes — B12 deficiency is the most common reversible coexisting cause (and is worsened by metformin).
Asymmetric, predominantly motor, or rapidly progressive neuropathy should raise concern for CIDP, vasculitis, or paraneoplastic causes — order NCS/EMG and additional workup; CIDP is treatable (IVIG, steroids).
Annual foot exam with 10-g monofilament + tuning fork is the highest-yield screening intervention to prevent amputation.
Glycemic control is most effective at preventing neuropathy progression in type 1 DM; effect is more modest in type 2.
Treatment-induced neuropathy of diabetes ('insulin neuritis') can occur with rapid A1c reduction — counsel patients before intensifying therapy.
Charcot foot may mimic cellulitis (red, warm, swollen, painless) — recognize and offload immediately; missed Charcot leads to amputation.
Cardiovascular autonomic neuropathy (resting tachycardia, blunted heart rate variability, orthostasis) is associated with increased mortality — consider beta-blocker cautiously.
Avoid combination of tramadol with SSRIs/SNRIs (serotonin syndrome) and watch for QT prolongation with TCAs and methadone.
Painful DPN responds to gabapentinoids, duloxetine, or TCAs — choose based on comorbidities (renal function, mood, cardiac status).

References

ADA 2022 — Diabetic Neuropathy: A Position Statement by the American Diabetes Association (Pop-Busui et al., Diabetes Care 2017; updates within Standards of Care)
AAN 2022 — Oral and Topical Treatment of Painful Diabetic Polyneuropathy: Practice Guideline Update (Price et al., Neurology 2022)
Toronto Consensus — Diabetic Neuropathies: Update on Definitions, Diagnostic Criteria, Estimation of Severity, and Treatments (Tesfaye et al., Diabetes Care 2010)
DCCT/EDIC — Effect of Intensive Diabetes Therapy on the Development and Progression of Neuropathy (DCCT Research Group, Ann Intern Med 1995)

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