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Toronto Notes 2019 Peripheral Neuropathies
• mononeuropathy:singlenervedeficit
■ carpal tunnel syndrome (most common): compression of median nerve at wrist
◆ symptoms: wrist pain, paresthesia first 3 and 1⁄2 digits, ± radiation to elbow, worse at night ◆ signs: Tinel’s sign, Phalen’s test, thenar muscle wasting, sensory deficit
◆ EMG/NCS: slowing at wrist (both motor and sensory)
◆ etiology: entrapment, pregnancy, DM, gammopathy, rheumatoid arthritis, thyroid disease
■ Bell’s palsy (most common cranial neuropathy): see Otolaryngology, OT22
■ Entrapment/compression: ulnar (compression at elbow), median (at pronator teres), radial (at
spiral groove of humerus), obturator (from childbirth), peroneal (due to crossing legs or surgical
positioning), posterior tibial (tarsal canal)
• mononeuropathymultiplex:deficitaffectingmultiplediscretenerves(asymmetric)
■ must rule out vasculitis or collagen vascular disease; consider MMN (multifocal motor neuropathy) or MADSAM (multifocal acquired demyelinating sensory and motor neuropathy)
• polyneuropathy:symmetricaldistalstocking-glovepattern
■ symmetrical distal sensorimotor deficit affecting longest fibres first (stocking-glove distribution),
hypotonia; progression of dysesthesia early and weakness later
■ etiology: DM (most common), renal disease, substances, toxins, genetics, SLE, HIV, leprosy, alcohol,
B12 deficiency, uremia
■ chronicinflammatorydemyelinatingpolyneuropathy(CIDP)
◆ chronic relapsing sensorimotor polyneuropathy with increase protein in CSF and demyelination (shown on EMG/NCS)
◆ course is fluctuating, in contrast with the acute onset of GBS
◆ treatment: first-line is prednisone; alternatives are plasmapheresis, IVIG, and azathioprine
Neurology N37
Axonal neuropathies have decreased amplitude on NCS; demyelinating neuropathies have decreased velocity on NCS
Ototoxic drugs (e.g. aminoglycosides) should not be given to diabetics
Sensory neuropathy of the feet prevent them from adequately compensating for loss of vestibular function
IVIG and plasmapheresis lead to more rapid improvement, less intensive care and less ventilation, but do not change mortality or relapse rate
Table 18. Differential Diagnosis of Symmetric Polyneuropathy
Vascular
Infectious
Immune
Hereditary Neoplastic
Toxin
Metabolic
Nutritional Other
Etiology
PAN
SLE
RA
HIV Leprosy
Lyme
GBS
CIDP
HMSN Paraneoplastic Myeloma
Lymphoma
Monoclonal gammopathy
EtOH
Heavy metals (i.e. lead)
Medications DM
Hypothyroidism Renal failure B12 deficiency Porphyria Amyloid
Mechanism
Ischemic
Ischemic
Ischemic Axonal/demyelination Infiltrative
Axonal/demyelination Demyelination Demyelination Axonal/demyelination Axonal/demyelination Axonal/demyelination
Axonal
Demyelination
Axonal Axonal
Axonal Ischemic/axonal
Axonal Axonal Axonal Axonal Axonal
Course
Chronic
Chronic Chronic Chronic Acute
Chronic Acute Chronic Chronic Chronic Chronic
Chronic
Chronic
Sub-acute Sub-acute
Sub-acute Chronic
Chronic Chronic Sub-acute Sub-acute Sub-acute
Modalities Investigations
S/M See Rheumatology, RH19 S/M See Rheumatology, RH11 S/M See Rheumatology, RH8 S/A HIV serology
S/A Leprosy serology Nerve biopsy
M Lyme serology
M LP (protein; nocells) S/M LP (protein)
S/M Genetic testing
S/M Paraneoplastic antibodies S/M SPEP
Skeletal bone survey
M SPEP
Bone marrow biopsy
S/M SPEP
Bone marrow biopsy
S/M GGT, MCV
S/M Urine heavy metals
S/M Drug levels
S/A Fasting glucose, HbA1c, 2 h OGTT
S/M TSH, T3, T4
S/A Electrolytes, Cr, BUN S/M Vitamin B12
M Urine porphyrins
S Nerve biopsy
Evaluation of Distal Symmetric Polyneuropathy: Role of Laboratory and Genetic Testing Neurology 2009;72:185-192
Screening Lab Tests: Blood glucose, serum B12 with metabolites, serum protein immunofixation electrophoresis.
Genetic Testing: Indicated for cryptogenic polyneuropathy exhibiting classic hereditary neuropathy phenotype. Screen for CMT1A duplication/deletion and Cx32 mutations.
A = autonomic; CIDP = chronic inflammatory demyelinating polyneuropathy; GGT = gamma-glutamyl transferase; HMSN = hereditary motor sensory neuropathy; M = motor; OGTT = oral glucose tolerance test; PAN = polyarteritis nodosa; RA = rheumatoid arthritis; S = sensory; SLE = systemic lupus erythematosus; SPEP = serum protein electrophoresis