Abstract
Peripheral neuropathy involving the feet and legs has emerged as one of the most prevalent and disabling neurological sequelae associated with acute and post-acute COVID-19 illness. Although initially overshadowed by respiratory manifestations of SARS-CoV-2 infection, neurological complications are now recognized as major contributors to morbidity, disability, diminished quality of life, and prolonged functional impairment. Distal sensory neuropathy, small fiber neuropathy, dysautonomia, painful paresthesias, gait instability, weakness, muscle wasting, and neurovascular dysfunction have been increasingly documented among individuals following both severe and mild COVID-19 infection.
This review synthesizes current knowledge concerning the etiology, physiology, pathology, clinical progression, diagnostic evaluation, and treatment of COVID-19–associated neuropathy affecting the lower extremities. Mechanistic pathways appear multifactorial and include immune dysregulation, endothelial injury, microvascular thrombosis, mitochondrial dysfunction, cytokine-mediated neurotoxicity, autoantibody formation, direct viral neuroinvasion, dysautonomia, metabolic disruption, and neuroinflammatory cascades. Small fiber neuropathy has emerged as a particularly prominent phenotype among long COVID patients, often occurring independently of overt electrophysiological abnormalities.
The clinical spectrum ranges from transient sensory disturbance to severe debilitating neuropathic syndromes involving autonomic instability and profound ambulatory dysfunction. Current therapeutic approaches remain largely symptomatic and supportive, although emerging evidence suggests potential benefit from immunomodulatory therapies in selected patients exhibiting autoimmune-mediated neuropathic phenotypes.
This article reviews evolving scientific literature while critically examining unresolved controversies and future research priorities in the rapidly developing field of COVID-related peripheral nerve disease.
Introduction
Since the emergence of SARS-CoV-2 in late 2019, COVID-19 has evolved from a predominantly respiratory illness into a complex multisystem disorder with profound neurological implications. Neurological manifestations are now recognized across both acute and chronic phases of disease. Among these complications, neuropathy affecting the lower extremities has become increasingly prevalent and clinically significant.
Patients commonly report burning feet, numbness, tingling, stabbing pain, electric shock sensations, fasciculations, gait instability, temperature dysregulation, weakness, and profound fatigue. Many individuals experience symptoms persisting months or years beyond initial infection. Such manifestations have become particularly associated with post-acute sequelae of SARS-CoV-2 infection (PASC), commonly termed “long COVID.”
Early pandemic attention focused primarily upon respiratory failure, acute respiratory distress syndrome (ARDS), and cardiovascular complications. However, as survival improved and longitudinal follow-up expanded, clinicians increasingly observed persistent neurological deficits among recovering patients. Peripheral neuropathy emerged as one of the most common neurological complaints.
Several studies have suggested that neuropathic symptoms occur in a substantial percentage of post-COVID individuals, with varying prevalence estimates depending upon methodology, patient population, and diagnostic criteria. Small fiber neuropathy, dysautonomia, and sensory-predominant neuropathies appear especially common.
Importantly, COVID-associated neuropathy differs in several respects from classic diabetic, toxic, or hereditary neuropathies. Many patients lack traditional neuropathy risk factors. Symptoms may fluctuate dramatically. Autonomic involvement is common. Electrophysiological studies may appear normal despite severe clinical symptoms. Immune-mediated mechanisms appear disproportionately important.
The feet and legs are especially vulnerable because of the extraordinary metabolic demands and anatomical length of peripheral axons supplying distal lower extremities. Long axons exhibit heightened susceptibility to ischemia, inflammatory injury, mitochondrial dysfunction, and microvascular compromise.
This review explores the current understanding of COVID-19–associated lower extremity neuropathy and examines emerging evidence regarding underlying biological mechanisms, diagnostic approaches, and therapeutic interventions.
Neurotropism of SARS-CoV-2
SARS-CoV-2 demonstrates significant neurotropic potential. Although debate persists regarding the extent of direct neural invasion, mounting evidence supports neurological involvement through both direct and indirect mechanisms.
The virus gains cellular entry primarily via angiotensin-converting enzyme 2 (ACE2) receptors. ACE2 receptors are widely expressed throughout the nervous system, including endothelial cells, glial cells, dorsal root ganglia, peripheral nerves, and autonomic structures.
Several pathways for nervous system involvement have been proposed:
- Hematogenous dissemination
- Retrograde axonal transport
- Trans-synaptic spread
- Endothelial invasion
- Immune-mediated secondary injury
- Blood-brain barrier disruption
- Cytokine-mediated neurotoxicity
Peripheral nerves may be injured even without direct viral invasion. Immune activation, inflammatory cytokines, vascular compromise, and autoantibody production appear capable of producing profound neuropathic syndromes independently of detectable viral particles within nerve tissue.
Anatomy and Physiology of Peripheral Nerves
Understanding COVID-related neuropathy requires appreciation of peripheral nerve structure and function.
Peripheral nerves consist of axons extending from neuronal cell bodies located within dorsal root ganglia or anterior horn cells. These axons are enveloped by Schwann cells and connective tissue layers including endoneurium, perineurium, and epineurium.
Large myelinated fibers mediate:
- Proprioception
- Vibration sensation
- Motor control
Small fibers mediate:
- Pain perception
- Temperature sensation
- Autonomic regulation
The distal lower extremities depend upon extraordinarily long axons extending from lumbar spinal cord segments to the feet. Such axons possess substantial metabolic requirements and are highly susceptible to:
- Hypoxia
- Ischemia
- Oxidative stress
- Mitochondrial dysfunction
- Immune attack
- Microvascular compromise
Peripheral nerves rely heavily upon intact microcirculation. Even subtle endothelial dysfunction or capillary thrombosis may impair axonal function.
Etiology of COVID-19–Associated Neuropathy
Immune Dysregulation
Immune-mediated injury appears central to many COVID-related neuropathies.
SARS-CoV-2 infection triggers profound activation of innate and adaptive immune pathways. In some individuals this response becomes dysregulated, producing sustained inflammatory activation and autoimmunity.
Potential mechanisms include:
- Molecular mimicry
- Bystander activation
- Epitope spreading
- Persistent antigenic stimulation
- Aberrant cytokine release
Autoantibodies targeting neural tissue have been detected in subsets of long COVID patients. Some exhibit antibodies against gangliosides, adrenergic receptors, muscarinic receptors, or other neural antigens.
Immune-mediated demyelination and axonal injury may occur through:
- Complement activation
- Macrophage infiltration
- Cytotoxic T-cell activity
- Cytokine-mediated neurotoxicity
This mechanism parallels known postinfectious neuropathies such as Guillain-Barré syndrome.
Cytokine-Mediated Neurotoxicity
COVID-19 may produce prolonged elevation of inflammatory cytokines including:
- IL-6
- TNF-alpha
- IL-1β
- Interferon gamma
These mediators exert direct neurotoxic effects.
Inflammatory cytokines can:
- Sensitize nociceptors
- Damage Schwann cells
- Impair axonal transport
- Disrupt mitochondrial function
- Increase oxidative stress
- Promote neuroinflammation
Persistent cytokine activation may help explain chronic neuropathic pain and dysautonomia in long COVID.
Endothelial Dysfunction and Microvascular Injury
Endothelial injury has emerged as a hallmark of COVID-19 pathology.
SARS-CoV-2 induces:
- Endothelial inflammation
- Capillary leakage
- Hypercoagulability
- Microthrombosis
- Reduced nitric oxide bioavailability
- Impaired autoregulation
Peripheral nerves are highly dependent upon microvascular perfusion. Small vessel dysfunction may produce ischemic injury affecting distal axons.
Skin biopsies from some long COVID patients demonstrate reduced capillary density and evidence of microvascular abnormalities.
Such mechanisms may contribute to:
- Burning feet
- Cold extremities
- Exercise intolerance
- Dysautonomia
- Distal sensory loss
Small Fiber Neuropathy
Small fiber neuropathy (SFN) has become one of the most recognized neurological manifestations of long COVID.
Small fibers include thinly myelinated A-delta fibers and unmyelinated C fibers responsible for:
- Pain
- Temperature sensation
- Sweating
- Vasomotor regulation
- Autonomic function
Symptoms include:
- Burning pain
- Tingling
- Electric shock sensations
- Allodynia
- Dysautonomia
- Orthostatic intolerance
Importantly, standard nerve conduction studies may remain normal because such tests primarily evaluate large myelinated fibers.
Diagnosis often requires:
- Skin biopsy
- Quantitative sensory testing
- Autonomic testing
Mechanisms underlying SFN may include:
- Autoimmunity
- Cytokine injury
- Neurovascular dysfunction
- Mast cell activation
- Mitochondrial impairment
Mitochondrial Dysfunction
Mitochondrial injury appears increasingly implicated in long COVID neuropathology.
Peripheral nerves possess exceptionally high energy demands. Mitochondrial dysfunction may impair:
- Axonal transport
- Ion channel regulation
- Neurotransmission
- Membrane stability
Potential mechanisms include:
- Oxidative stress
- Persistent inflammation
- Viral protein toxicity
- Impaired oxygen utilization
- Microvascular ischemia
Mitochondrial dysfunction may help explain:
- Exercise intolerance
- Post-exertional malaise
- Muscle fatigue
- Neuropathic pain
- Weakness
Dysautonomia and Peripheral Neuropathy
Autonomic dysfunction frequently accompanies COVID-related neuropathy.
Common manifestations include:
- Orthostatic intolerance
- Tachycardia
- Temperature dysregulation
- Sweating abnormalities
- Gastrointestinal dysmotility
- Vasomotor instability
Postural orthostatic tachycardia syndrome (POTS) has become increasingly recognized after COVID infection.
Autonomic small fibers appear particularly vulnerable to inflammatory and immune-mediated injury.
Clinical Manifestations
Sensory Symptoms
Patients commonly describe:
- Burning feet
- Tingling
- Numbness
- Pins-and-needles sensations
- Electric shocks
- Vibratory sensations
- Crawling sensations
- Hyperesthesia
- Allodynia
Symptoms frequently worsen at night.
Motor Symptoms
Motor involvement may include:
- Weakness
- Muscle wasting
- Foot drop
- Fasciculations
- Cramping
- Reduced endurance
- Impaired balance
Severe cases may significantly impair ambulation.
Autonomic Symptoms
Autonomic involvement may manifest as:
- Orthostatic dizziness
- Palpitations
- Heat intolerance
- Cold feet
- Color changes
- Sweating abnormalities
- Gastrointestinal dysfunction
Pain Syndromes
Neuropathic pain may become severe and disabling.
Patients often describe:
- Burning
- Stabbing
- Crushing
- Freezing
- Electrical sensations
Pain severity frequently appears disproportionate to objective findings.
Pathology
Histopathological findings vary considerably.
Reported abnormalities include:
- Axonal degeneration
- Reduced intraepidermal nerve fiber density
- Endoneurial inflammation
- Microvascular injury
- Schwann cell damage
- Complement deposition
- Perivascular lymphocytic infiltration
Small fiber loss is particularly prominent in many biopsy studies.
Diagnostic Evaluation
Clinical Assessment
Comprehensive neurological examination remains essential.
Evaluation should assess:
- Sensory deficits
- Reflexes
- Motor strength
- Gait
- Coordination
- Autonomic signs
Electrophysiological Testing
Nerve conduction studies and electromyography may reveal:
- Axonal neuropathy
- Demyelination
- Reduced amplitudes
- Slowed conduction velocity
However, studies may remain normal in small fiber neuropathy.
Skin Biopsy
Skin biopsy assessing intraepidermal nerve fiber density is increasingly important.
Reduced fiber density supports small fiber neuropathy diagnosis.
Autonomic Testing
Autonomic evaluation may include:
- Tilt-table testing
- QSART
- Heart rate variability
- Sweat testing
Laboratory Evaluation
Evaluation should exclude alternative neuropathy causes:
- Diabetes
- Vitamin deficiencies
- Thyroid disease
- Autoimmune disorders
- Toxins
- Monoclonal gammopathies
Inflammatory markers and autoimmune panels may provide supportive evidence.
Differential Diagnosis
COVID-associated neuropathy must be distinguished from:
- Diabetic neuropathy
- Chronic inflammatory demyelinating polyneuropathy
- Guillain-Barré syndrome
- Vitamin deficiency neuropathy
- Toxic neuropathy
- Vasculitic neuropathy
- Fibromyalgia
- Functional neurological disorder
Clinical Course
Clinical progression varies substantially.
Some patients improve within weeks.
Others experience:
- Persistent symptoms
- Relapsing-remitting patterns
- Progressive disability
- Chronic pain syndromes
Long COVID neuropathy may fluctuate dramatically, often worsening after physical or cognitive exertion.
Treatment Approaches
Symptomatic Pharmacotherapy
Common medications include:
- Gabapentin
- Pregabalin
- Duloxetine
- Amitriptyline
- Nortriptyline
- Topical lidocaine
- Capsaicin
Response varies widely.
Immunomodulatory Therapy
Selected patients may benefit from:
- Intravenous immunoglobulin (IVIG)
- Corticosteroids
- Plasma exchange
Evidence remains limited but evolving.
Physical Rehabilitation
Rehabilitation strategies include:
- Balance training
- Gait therapy
- Strengthening
- Orthotics
- Occupational therapy
Overexertion should be avoided in patients with post-exertional symptom exacerbation.
Autonomic Management
Interventions may include:
- Hydration
- Salt loading
- Compression garments
- Beta blockers
- Fludrocortisone
- Midodrine
Nutritional and Metabolic Support
Potential supportive interventions include:
- Vitamin B12
- Alpha-lipoic acid
- Acetyl-L-carnitine
- Coenzyme Q10
Robust evidence remains limited.
Emerging Research Directions
Current research priorities include:
- Biomarker identification
- Autoantibody characterization
- Neuroimaging advances
- Immune phenotyping
- Therapeutic trials
- Longitudinal cohort studies
Better mechanistic understanding remains urgently needed.
Controversies and Unresolved Questions
Major unresolved issues include:
- Persistence of viral reservoirs
- Autoimmune versus inflammatory dominance
- Optimal immunotherapy timing
- Long-term prognosis
- Relationship between vaccination and neuropathic syndromes
- Genetic susceptibility
The heterogeneity of long COVID suggests multiple overlapping pathogenic pathways.
Public Health Implications
COVID-associated neuropathy may produce substantial societal burden through:
- Disability
- Lost productivity
- Chronic pain
- Healthcare utilization
- Psychological distress
Recognition of neurological sequelae remains essential for healthcare planning.
Conclusion
COVID-19–associated neuropathy involving the feet and legs represents a significant and increasingly recognized neurological complication of SARS-CoV-2 infection. Emerging evidence supports multifactorial mechanisms involving immune dysregulation, endothelial dysfunction, microvascular injury, neuroinflammation, mitochondrial impairment, dysautonomia, and small fiber degeneration.
Clinical manifestations range from mild paresthesias to profoundly disabling neuropathic syndromes with severe autonomic dysfunction and impaired mobility. Small fiber neuropathy appears especially prevalent among long COVID patients and may evade conventional electrophysiological testing.
Although treatment remains largely symptomatic, evolving research into immune-mediated mechanisms may eventually yield targeted therapeutic strategies. Continued investigation is essential to clarify pathogenesis, optimize diagnostic criteria, and develop evidence-based interventions for affected individuals.
COVID-related neuropathy is likely to remain a major neurological and public health challenge for years to come.