Subacute inflammatory demyelinating polyneuropathy (SIDP) is a subacute progressive symmetric sensorial and/or motor disorder characterized by muscular weakness with impaired sensation, absent or diminished tendon reflexes and elevated cerebrospinal fluid (CSF) proteins. SIDP is an intermediate form between Guillain-Barré syndrome (GBS) and chronic inflammatory demyelinating polyneuropathy (CIDP; see these terms).