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Hereditary motor sensory neuropathies (HMSN)/ Charcot-Marie Tooth (CMT)
Hereditary motor sensory
neuropathies (HMSN)/
Charcot-Marie Tooth (CMT)
Definition
Genetic neurological disorder
of progressive motor +/-
sensory loss in peripheral nerves
Prognosis
Chronic condition, but
rarely lose ability to walk
Pathophysiology
Defect
Genetic disorder (AD, AR, X-linked types; also de novo) causing mutation in myelin genes e.g. CMT1A
Mechanism
Length dependent wasting of peripheral nerves, resulting in peripheral muscles being affected first
Ascending muscle wasting, may affect sensation
Epidemiology
Rare
AD inheritance
Starts in puberty
Clinical
presentation
Motor weakness
Predominantly distal muscles
Sensation change
Numbness, tingling, pins and needles
Burning, stabbing
Balance issues
Sensory ataxia
Diagnosis
Examination
Neuro
Motor: distal weakness bilaterally, wasting, fasiculation; atrophy of peroneal muscles (champagne bottle legs), foot drop common
Sensation: reduced sesation glove+stocking distribution, reduced vibration sense, reduced joint position
Reflexes: reduced ankle jerks
Investigations
Bloods
FBC (infection), CRP/ESR (inflammation), U+E (CKD), LFTs,
vitamin B12/thymine/folate (deficiency)
Toxin screen (lead, alcohol)
Autoimmune screen (ANA, ANCA)
Paraneoplastic screen
Genetic testing (CMT)
CSF
High protein (demyelination)
Bedside
Obs (check if autonomic neuropathy)
Special tests
NCS, EMG (demyelinating vs axonal causes)
Biopsy
Peripheral nerve biopsy (onion bulb formation)
History
DH
Meds, allergies
FH
CMT disease, other neurological disease
PMH
Known medical conditions, surgery
SH
Occupation, living arrangements,
smoking, alcohol, drugs
PC/HPC
Distal weakness of arms/legs, wasting
Reduced sensation in glove and stocking distribution
Differentials
Motor
Infection: GBS, CIDP, Lyme
Autoimmune: vasculitis
Metabolic: Lead poisoning, porphyria
Sensory
Infection: leprosy
Autoimmune: amyloidosis, vasculitis
Metabolic: DM, B12/folate deficiency, CKD, hypothyroidism
Neoplastic: paraneoplastic syndrome
Drugs: alcohol, anti-TB drugs, chemotherapy
Management
Conservative
Information, advice, support
Neurology referral