Subacute Inflammatory Demyelinating Polyneuropathy

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).

Clinical description

The time to maximum severity (nadir) and the subsequent course of SIDP differentiate it from GBS and CIDP. Onset can occur at any age but is more common between the 4th and 5th decades. When onset is in childhood, SIDP is rather considered as CIDP. Males are predominantly affected. Patients present a 4 to 8 week history of progression of monophasic demyelinating neuropathy (DN) associated with the occurrence of a symmetric progressive weakness in both proximal and distal muscles with impaired sensation and absent/diminished tendon reflexes. Neuropathy is symmetric and can be either sensorimotor or pure motor in nature. Rarely, cranial nerve dysfunction and respiratory failure may occur.

Etiology

SIDP, like CIDP, could be due to an immune reaction, resulting in segmental demyelination which may induce a concomitant axonal loss.

Diagnostic methods

Diagnosis is based on clinical and electrophysiological findings. CSF analysis and histological findings can provide additional supportive data but are not mandatory. Four diagnostic criteria allow definite diagnosis: progressive motor and/or sensory dysfunction consistent with neuropathy in more than one limb with time to nadir between 4 to 8 weeks, electrophysiological evidence of demyelination at least in 2 nerves (EMG and nerve conduction study), no other etiology of neuropathy and no relapse on adequate follow-up (in the absence of this last criterion, a probable SIDP is diagnosed). In addition, supportive criteria include raised CSF proteins and segmental and multifocal demyelination in nerve biopsy (in clinically suspected SIDP cases in which electrophysiological proof of demyelination is absent). Cytoalbuminologic dissociation in CSF is characteristic, pointing to nerve root involvement. Occasionally, CSF studies reveal mild lymphocytic pleocytosis and elevated gamma globulins. SIDP presents mostly the same clinical manifestations as CIDP with 3 exceptions: a higher rate of history of infection (about 40% of cases), no relapsing course and a higher rate of recovery to normal.

Differential diagnosis

Differential diagnosis includes GBS and rarely some other acquired polyneuropathies (monoclonal gammopathy (see this term), infections, or systemic inflammatory or immune-mediated diseases, toxic neuropathies, neuropathy due to nutritional deficiency).

Management and treatment

Most patients respond to steroid therapy (prednisone). A few cases may also require intravenous immunoglobulins (IVIg) and/or plasmapheresis.

Prognosis

The earlier treatment begins in the course of the disease, the higher the rate of recovery to normal (70%) and 30% of patients have partial recovery; some of these cases may progress to CIDP. Rare cases of spontaneous remission have also been reported.