- 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
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SCN9A
; Chromosome 2q24.3; Dominant or Sporadic
- Genetics
- Mutations
13
- Missense
- F216S, S241T, N395K, I848T, L858H,
L858F, Pro610Thr, R1150W
- Later onset (2nd decade) disease: Q10R; I136V
- Sporadic case: Mosaic in father
- Allelic disorders
- Recessive
- Dominant
- Polymorphisms
- 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
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