Abstract Introduction Altered mental status (AMS) in association with rigidity presents a critical diagnostic challenge generally requiring intensive care unit (ICU) level of care. Early management has a relatively consistent approach across the differential and can be initiated while collecting the studies needed to identify the underlying cause. We present a case highlighting this initial management and diagnostic reasoning, ultimately diagnosed with paraneoplastic Stiff Person Syndrome (SPS) secondary to prostate adenocarcinoma, a malignancy association which has not previously been reported in the literature. Description of Case A 72-year-old man with a history of metastatic prostatic adenocarcinoma (previously treated with docetaxel, currently on abaterone and prednisone), chemotherapy-related peripheral neuropathy and recent unilateral diplopia with multiple ground level falls presents with several days of worsening bilateral lower extremity weakness and AMS. Brain imaging was unremarkable and electroencephalogram showed diffuse background slowing. On exam, he was found to have significant rigidity most pronounced in his bilateral lower extremities. He required intubation and scheduled benzodiazepines with monitoring of creatine kinase. Initial cerebrospinal fluid (CSF) studies showed lymphocytic pleocytosis, raising suspicion for an autoimmune encephalitis, treated with high dose steroids and intravenous immunoglobulin. CSF antibody studies eventually returned with GAD65 antibodies and high titers (1:30,000) of ampiphysin antibodies, consistent with paraneoplastic SPS. The patient improved, was extubated, and discharged home with plans for ongoing immunosuppression. Discussion AMS and rigidity together generate a rather specific differential diagnosis (see table). It is important for the diagnostician to differentiate between spasticity, which can have direction and velocity-dependent resistance, and rigidity, which is consistent throughout a movement but may include cogwheeling when combined with a tremor. While the causes of rigidity and AMS together can be diverse, initial management has significant overlap and should be initiated promptly. This includes control of rigidity with benzodiazepines to reduce rhabdomyolysis, consideration of dantrolene and bromocriptine, airway protection, and intravenous fluids for renoprotection. Additional considerations include treatment of hypertensive emergency, hyperthermia, discontinuation of serotonergic medications and release of dopamine blockade. Diagnostic studies should include head imaging, electroencephalogram, and CSF studies with autoimmune encephalitis and prion disease panels. Paraneoplastic causes should be considered in patients with any cancer history, even if the malignancy is not typically associated with neurologic paraneoplastic syndromes. To date, prostate adenocarcinoma has not been previously reported in the literature as an associated malignancy for paraneoplastic SPS, which is most associated with breast and small cell lung cancer. This abstract is funded by: None
Einspahr et al. (Fri,) studied this question.