Objective: To report a case of immune-mediated stiff limb syndrome referred for extremity focal dystonia.

Background: Autoantibodies to glutamic acid decarboxylase (GAD) are associated with multiple neurological disorders, most commonly cerebellar ataxia and stiff-person syndrome (SPS).[1] Antibodies to GAD are also commonly seen in other immunologic disorders, such as type I Diabetes Mellitus (DM). A more rare clinical subtype of SPS, stiff-limb-syndrome, can occur in ~10-15% of cases, and typically presents with focal involvement of a lower limb with sparing of the trunk muscles.

Method: The patient is a 33 y/o male with a PMH of type 1 DM who presented with subacute onset (months) of abnormal movement involving the right foot, ankle, and toes with associated pain, discomfort, and stiffness. His neurologic exam was notable for persistent right great toe extension at the MTP joint and great toe flexion at the interphalangeal joint. Digits 2-5 also showed increased flexion, but to lesser extent. His tone was increased in the distal RLE most consistent with rigidity, particularly at the ankle. Otherwise his neurologic exam showed no other focal deficits.

Results: MRI brain with and without contrast showed no focal intracranial abnormalities. EMG/NCS of the L3-S1 sampled muscles of the right lower extremity found inability to fully silence the flexor hallucis longus and extensor hallucis longus muscles. Laboratory evaluation was positive for serum GAD antibodies (>250.0; normal 0-5). Lumbar puncture showed positive CSF GAD65 antibodies (2.30; normal range <0.02), 1 oligoclonal band (normal 0-1), slightly elevated glucose (91; normal 50-80), normal IgG Index (0.52; normal 0.28-0.66), normal protein (22; normal 15-45), and no cellular infiltrate. CT chest/abdomen/pelvis showed no clear underlying malignancy. The patient was treated with low dose clonazepam 0.5mg BID and has noted a significant symptomatic improvement in his lower extremity spasm, pain, and stiffness.

Conclusion: We report a case of stiff-limb-syndrome referred for evaluation for a focal lower extremity dystonia and pain associated with positive serum and CSF anti-GAD antibodies in a patient with type 1 DM. Even though this entity is rare, it is still important to consider anti-GAD antibody in the differential diagnosis of a focal dystonia with associated pain in a young patient of subacute-to-chronic onset, especially with a history of type 1 DM

References: 1.) Baizabal-Varvallo, JF; Alonso-Juarez, M. Cerebellar disease associated with anti-glutamic acid decarboxylase antibodies: review. J Neural Transm. 2017 Oct;124(10):1171-1182.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/stiff-limb-syndrome-masquerading-as-a-focal-limb-dystonia/