Stiff-person spectrum disorder induced by shingles: a case report.

Background: Stiff-person spectrum disorder (SPSD) is a rare autoimmune neurological disorder characterised by progressive rigidity, muscle co-contractions and spasms; 5%-10% are paraneoplastic. Few infection-related SPSD cases have been reported. Case presentation: We describe a 56-year-old woman who developed SPSD after herpes zoster. Eight days after rash onset, she experienced persistent lower-limb tonic spasms with co-contractions, autonomic symptoms and elevated anti-glutamic acid decarboxylase antibodies in serum and cerebrospinal fluid. Immunotherapy with repeated high-dose intravenous immunoglobulin and methylprednisolone pulses, along with continuous benzodiazepines and epidural analgesia, led to gradual improvement over 3 months. Conclusions: Pain from herpes zoster may have amplified muscle co-contractions via withdrawal and crossed extension reflexes, exacerbating impaired reciprocal inhibition in SPSD. Clinicians should consider optimal pain control in addition to immunotherapy for SPSD triggered by infection.