Disorder of the peripheral nerves that primarily impair small nerve fibers. The affected small nerve fibers include myelinated A-delta fibers (see A FIBERS) and unmyelinated C FIBERS. Because these small fibers innervate skin and help control autonomic function, their neuropathy presents with neuropathic pain, reduced thermal and pain sensitivity, and autonomic dysfunction (e.g. abnormal sweating or facial flushing). Small fiber neuropathy can be idiopathic or associated with underlying diseases (e.g., AMYLOIDOSIS; DIABETES MELLITUS; SARCOIDOSIS; or VASCULITIS).