A case of possible stiff person syndrome (SPS) / Progressive encephalomyelitis with rigidity and myoclonus (PERM) misclassified as catatonia

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Stiff person syndrome (SPS) is a rare neurological disorder manifesting as profound stiffness and rigidity. It is believed to be caused by autoantibodies against antigens involved in the synthesis and release of Gamma-aminobutyric acid (GABA) – a major inhibitory neurotransmitter of the central nervous system (CNS). Progressive encephalomyelitis with rigidity and myoclonus (PERM), also known as SPS-plus syndrome, has more extensive involvement of the CNS and autonomic nervous system. Diagnosis of SPS has become largely reliant on the detection of antibodies in the serum and CSF. However, existing literature suggests that up to one third of cases of SPS have no known antibody positivity. This case report describes a presentation of presumed antibody negative SPS which was initially misclassified as catatonia. It aims to highlight the need for improved diagnostic criteria and increased recognition of SPS, as many patients with this syndrome live disabled for years before they are diagnosed and treated.