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Toronto Notes 2019 Pain Syndromes Myotonic Dystrophy
Etiology and Pathophysiology
• unstabletrinucleotide(CTG)repeatinmyotonicdystrophykinasegene(proteinkinase)at19q13.3, number of repeats correlates with severity of symptoms, autosomal dominant
Epidemiology
• mostcommonadultmusculardystrophy,prevalence3-5/100,000
Clinical Features
• appearance:ptosis,bifacialweakness,frontalbaldness(includingwomen),triangularfacegivinga drooping/dull appearance
• physicalexam
■ distribution of weakness: distal weaker than proximal (in contrast to other myopathies), steppage
gait
■ myotonia: delayed relaxation of muscles after exertion (elicit by tapping on thenar muscles with
hammer)
■ cardiac: 90% have conduction defects (1o heart block; atrial arrhythmias)
■ respiratory: hypoventilation 2o to muscle weakness
■ ocular: subcapsular cataracts, retinal degeneration, decreased intraocular pressure
■ other: DM, infertility, testicular atrophy
■ EMG: subclinical myotonia – long runs with declining frequency and amplitude
Treatment
• managementofmyotonia:phenytoin
Prognosis
• nocure,progressive,deathusuallyaround50yr
Pain Syndromes
Approach to Pain Syndromes
Definitions
• nociceptivepain:painarisingfromnormalactivationofperipheralnociceptors
• neuropathicpain:painarisingfromdirectinjurytoneuraltissue,bypassingnociceptivepathways • spontaneouspain:unprovokedburning,shooting,orlancinatingpain
• paresthesia:spontaneousabnormalnon-painfulsensation(e.g.tingling)
• dysesthesia:evokedpainwithinappropriatequalityorexcessivequantity
• allodynia:adysestheticresponsetoanon-noxiousstimulus
• hyperalgesia:anexaggeratedpainresponsetoanoxiousstimulus
Non-Pharmacological Management
• physical(PT,acupuncture,chiropracticmanipulation,massage)
• psychoeducational(CBT,familytherapy,education,psychotherapy)
Medical Pain Control
• combinationmulti-modaltherapyisimportant
• primaryanalgesics:acetaminophen,NSAIDs(oftenusedforsofttissueinjuries,strains,sprains,
headaches, and arthritis), opiates
• adjuvants: antidepressants (TCAs, SSRIs), anticonvulsants (gabapentin, carbamazepine, pregabalin),
baclofen, sympatholytics (phenoxybenzamine), α2-adrenergic agonists (clonidine)
Surgical Pain Control
• peripheralablation:nerveblocks,facetjointdenervation
• directdelivery:implantablemorphinepump
• centralablation:stereotacticthalamotomy,spinaltractotomy,ordorsalrootentrylesion • DBSordorsalcolumnstimulation
Neuropathic Pain
Definition
• painresultingfromadisturbanceoftheCNSorPNS
Epidemiology
• affectsupto6%ofpeople(2millionCanadians)
Neurology N41
• Pinprick sensation mediated by Aδ fibres • Pain due to tissue damage is mediated by
C fibres
WHO Pain Ladder
• Mild Pain: Non-opioid (acetaminophen
and/or NSAID) ± adjuvant
• Moderate Pain: Opioid for mild to
moderate pain (codeine/oxycodone) +
non-opioid ± adjuvant
• Severe Pain: Opioid for moderate to severe pain (morphine/hydromorphone) + non-opioid ± adjuvant
Axonal regeneration is directed by intact nerve sheaths; if the nerve sheath is damaged, axons grow without direction, become tangled, and form a neuroma. This can result in ectopic electrical impulses and neuropathic pain