Small fibre sensory neuropathy SFSN a.k.a. small fibre neuropathy SFN
- Small fibre involvement:
- Neuropathic pain; allodynia, hyperalgesia
- Reduced sensation to pin prick and temperature.
- Absence of large fibre involvement: light touch, vibratory, proprioceptive sensory loss or absent deep tendon reflexes
- Normal motor exam
Findings on Investigations:
+Electrodiagnosis NCS (sensory +motor +F waves) +/-EMG:
+Quantitative sensory testing QST:
- This is used to determine the patients threshold for sensory stimuli (pain, cold, warm and vibration sensation) and comparing them to normative data.
- Immunohistochemistry: polyclonal anti-protein-gene-product 9.5 antibodies (this stains nerve fibres in the skin) to assess Intra-Epidermal nerve fibre density IENF: reduced.
Na channel mutations in small fiber neuropathy
Investigations to consider:
- Fasting blood glucose, HBA1c, TFTs, Lipid profile, ESR, CRP, ANA screen, ENA panel (anti- dsDNA, anti-Sm, anti-RNP, SSA, SSB, anti-Jo-1, antitopoisomerase ‘formerly anti Scl-70’, antinucleolar, anticentromere), ANCA (c-ANCA, p-ANCA), Complement C3, C4 and CH50
- Infection tests: influenza, HIV
- Paraneoplastic tests: anti-Hu Antibodies
- Test for amyloidosis e.g. sural nerve biopsy.
- Autonomic neuropathy testing
- Genetic testing for hereditary amyloid neuropathies
- Approach to sensory deficits, neuromuscular diseases patterns, polyneuropathy, autonomic neuropathy, autonomic function testing,
- Tangier disease (high density lipoprotein HDL deficiency), familial amyloid polyneuropathy, non-hereditary amyloid neuropathy, sensorimotor polyneuropathy,
- Shy ME, Frohman EM, So YT, Arezzo JC, Cornblath DR, Giuliani MJ, Kincaid JC, Ochoa JL, Parry GJ, Weimer LH; Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology. Quantitative sensory testing: report of the Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology. Neurology. 2003 Mar 25;60(6):898-904.