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Original Investigation |

Childhood Onset of Stiff-Man Syndrome

Stacey L. Clardy, MD, PhD1; Vanda A. Lennon, MD, PhD1,2,3; Josep Dalmau, MD, PhD4,5; Sean J. Pittock, MD1,2; H. Royden Jones Jr, MD6; Deborah L. Renaud, MD1,7; Charles M. Harper Jr, MD1; Joseph Y. Matsumoto, MD1; Andrew McKeon, MD1,2
[+] Author Affiliations
1Department of Neurology, College of Medicine, Mayo Clinic, Rochester, Minnesota
2Department of Laboratory Medicine and Pathology, College of Medicine, Mayo Clinic, Rochester, Minnesota
3Department of Immunology, College of Medicine, Mayo Clinic, Rochester, Minnesota
4Department of Neurology, Hospital Clinic, Universitat de Barcelona/Institut d’investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Barcelona, Spain
5Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain
6Department of Neurology, Boston Children’s Hospital, Harvard Medical School, Boston, Massachusetts
7Department of Pediatrics, College of Medicine, Mayo Clinic, Rochester, Minnesota
JAMA Neurol. 2013;70(12):1531-1536. doi:10.1001/jamaneurol.2013.4442.
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Importance  Reports of pediatric-onset stiff-man syndrome (SMS) are rare. This may be an underrecognized disorder in child neurology practice.

Objective  To describe patients with disorders in the SMS spectrum beginning in childhood.

Design, Setting, and Participants  This study was a medical record review and serological evaluation conducted at child and adult neurology clinics at the Mayo Clinic, Rochester, Minnesota. Systematic review of the literature was conducted of patients who presented from 1984-2012 with onset of symptomatic SMS occurring at age 18 years or younger.

Main Outcomes and Measures  Response to symptomatic and immunotherapies, patient and physician reported, including modified Rankin scale.

Results  We identified 8 patients with childhood-onset SMS, representing 5% of patients with SMS evaluated at Mayo Clinic during a period of 29 years (4 were girls). The median age at symptom onset was 11 years (range, 1-14 years). The diagnosis in 3 patients was not established until adulthood (median symptom duration at diagnosis, 14 years; range, 0-46 years). The phenotypes encountered were: classic SMS (n = 5, involving the low back and lower extremities), variant SMS (n = 2, limited to 1 limb [with dystonic posture] or back), and progressive encephalomyelitis with rigidity and myoclonus (n = 1). Initial misdiagnoses included functional movement disorder (n = 2), generalized dystonia and parkinsonism (n = 1), and hereditary spastic paraparesis (n = 1). Six patients had 1 or more coexisting autoimmune disorders: type 1 diabetes mellitus (n = 4), thyroid disease (n = 2), and vitiligo (n = 2). Serologic study results revealed glutamic acid decarboxylase 65–IgG in all cases (median value, 754 nmol/L; range, 0.06-3847 nmol/L; normal value, ≤0.02 nmol/L) and glycine receptor antibody in 3 cases. Improvements were noted with symptomatic therapy (diazepam, 6 of 6 patients treated, and oral baclofen, 3 of 3 treated) and immunotherapy (intravenous immune globulin, 3 of 4 treated and plasmapheresis, 3 of 4 treated). The 3 patients with glycine receptor antibody all improved with immunotherapy. At last follow-up, 4 patients had mild or no symptoms, but 4 had moderate or severe residual symptoms and required maintenance symptomatic therapy (n = 5) and immunotherapy (n = 4). Ten of 12 pediatric SMS cases identified by literature review had a severe whole-body phenotype resembling progressive encephalomyelitis with rigidity and myoclonus.

Conclusions and Relevance  Childhood-onset SMS is a rare but underrecognized and treatable disorder. Serological and electrophysiological testing aid diagnosis.

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