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NEUROPATHIES: PAINFUL

Types
  Acute onset
  Diabetic amyotrophy
  Hereditary
  Idiopathic neuropathies
  Immune
  Local neuropathies
  Metabolic
  Mononeuritis multiplex
  Motor
  Small fiber
    Erythromelalgia
  Toxic

Other
  Axonal classifications
  Nociceptors
  Pain: General principles
  Pain medications

Also see
  Itch
  Muscle Pain
    Principles

From Roxane Institute

PAINFUL NEUROPATHIES: Differential Diagnosis


Sensory polyneuropathy syndromes: Idiopathic

Acute onset
Small fiber
  Neuropathy, Chronic
  Neuronopathy

Post surgical localized pain syndromes


α-Galactosidase Deficiency (Fabry disease) 20

  α-Galactosidase ; Chromosome Xq22.1; Recessive

Burning Mouth Syndrome 7


Erythromelalgia (Erythermalgia) 5

  • General definition: Intermittent burning pain in distal extremities
    • Especially hands and feet
    • In response to warm stimuli or exercise
    • Described & named by S. Weir Mitchell in 1878
  • Classifications
    • Primary idiopathic
    • Secondary
    • Familial Polyneuropathy & Erythromelalgia
    • Familial erythermalgia
        SCN9A ; Chromosome 2q24.3; Dominant or Sporadic
      • Genetics
      • SCN9A protein (NENA; PN-1; Nav1.7)
        • Sodium channel
          • Type 1: α-subunit
          • Tetrodotoxin-sensitive
        • Locations
          • Peripheral nerve
            • Nociceptive dorsal root ganglion cells
            • Distal neurites
            • May accumulate in neuromas
          • Sympathetic neurons
          • Not muscle or brain
        • Molecular Functions 5
          • Slow closed-state inactivation
          • Amplify small depolarizations (generator potentials)
            • Produces threshold currents
          • Mutant protein: Gain of function
            • Hyperpolarizing shift in channel activation
            • Increased amplitude of response to slow, small depolarizations
            • Cells expressing mutant protein are hyperexcitable
        • Associated sensory modalities 22
          • Pain
          • C-low threshold mechanoreceptors (C-LTMR)
            • Sensory modalities
              • Mechanical threshhold
              • Affective touch
              • Non-noxious cooling
            • Axon properties
              • Respond to low threshold punctate indentations
              • Conduction velocities in C-fibre range
              • Molecular: Tyrosine hydroxylase
              • 10% of dorsal root neurons
              • Skin: Longitudinal lanceolate endings surrounding hair follicles.
          • Inflammatory pain
    • Secondary to associated disease
      • Onset: Middle age
      • Associated disorders
        • Thrombocythemia (Myeloproliferative disorders)
          • Most typical
          • ? Related to intravascular platelet aggregation
            • Thrombotic occlusions of arterioles & small arteries
            • Platelet-mediated
              • Arteriolar inflammation
              • Fibromuscular intimal proliferation
        • Diabetes
        • Systemic autoimmune
          • Rheumatoid arthritis
          • Sjgren syndrome
          • Systemic lupus erythematosus
          • Vasculitis
        • Drugs
          • Iodine contrast
          • Calcium channel blockers
          • Bromocriptine
          • Cyclosporine
          • Norephedrine
          • Isopropranolol, topical
          • Pergolide
          • Statins (rosuvastatin; simvastatin)
        • Other neuropathies
          • Fabry
          • Hematologic
          • Infections
      • Clitocybe acromelalga mushroom poisoning
    • Localized: ? ABC variant of complex regional pain syndrome
  • Clinical
    • Onset age: Children & Adults; Usually before age 6 years
    • Pain
      • Location
        • Early: Distal extremities; Legs > Arms; Relative sparing of toes
        • Bilateral; Symmetric
        • May spread to hands, ear lobes & nose tip
      • Quality: Burning & Hot
      • Dysesthesias with touch
      • Environmental factors: Opposite responses to Raynauds
        • Exacerbated by: Heat; Standing; Exercise
        • Relief by: Cold; Elevation of extremity
      • Associated with warmth & flushing of extremity
    • Skin
      • Red & Warm in limbs
        • Initially: During attacks
        • May become constant
      • Itch: Episodic; May be followed by pain
    • Skeletal: Short toes & toenails
    • Disease course
      • Episodic
      • Severity of attacks may increase with age
      • Area involved by attacks may increase
    • Treatment
      • Aspirin may produce rapid (1 hour) short-lived improvement: 2° syndromes
      • Pain control: Capsaicin + Systemic analgesia
      • Cooling of affected limbs
      • Combination Gel 15
        • 1% Amitriptyline HCl +
        • 0.5% Ketamine HCl in pluronic lecithin organogel
        • Applied 4x to 5x daily
      • ? Epidural anesthesia
      • Treatment of associated disorder
    • Rule out
  • Laboratory
    • Skin biopsy: May be normal
  • Pathophysiology
    • ? Hyperactive axon reflex in C-nociceptor fibers
    • Skin pathology: Nonspecific; ? Reduction in autonomic plexi


Burning Feet Syndrome 1

  SCN9A ; Chromosome 2q24.3; Dominant

Small Fiber Neuropathy 5

  SCN9A ; Chromosome 2q24.3; Dominant

Episodic pain syndrome, Familial 1 (FEPS1)

  Transient receptor potential cation channel, Subfamily A, MEMBER 1 (TRPA1) ; Chromosome 8q13.3; Dominant

Reflex Sympathetic Dystrophy (Complex regional pain syndrome)


Tinel 1918
Causalgia after
median nerve lesion



Chronic Mountain Sickness 3


Patient information

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References
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21. Muscle Nerve 2021 Feb 5
22. Brain 2022;145:3637-3653
23. Brain Commun 2024 Apr 3
24. Brain Commun 2024;6(3):fcae155

9/13/2024