A 52-year-old man with a history of hypertension and a thymic neoplasm presented with subacute development of bilateral lower extremity weakness, dyspnea, and gait difficulty. Physical exam demonstrated mild weakness in bilateral lower extremities, along with concurrent spasticity and hyperreflexia in all muscle groups of his lower extremities. He exhibited 4+ patellar reflexes and a sustained ankle clonus bilaterally. Additionally, fasciculations in lower extremities were noted. His sensory exam was unrevealing. Imaging of his neuro-axis did not demonstrate any obvious structural etiology of his symptoms. Serological testing confirmed antibody positivity for both Acetylcholine Receptor Antibodies (Ach R binding Ab, 1.09 nmol/L) and anti-GAD Ab (>120 IU/mL). A clinical diagnosis of SPS was made. The patient was treated initially with IVIG and diazepam, followed by an eventual thymectomy leading to sustained clinical improvement.

It is estimated that about one-third of patients with thymomas will have an associated paraneoplastic syndrome (PNS), most commonly myasthenia gravis. A paraneoplastic-variant of SPS is rare and accounts for 5-10% of all cases. Thymoma resection often improves symptoms; however, patients need monitoring for recurrence or new paraneoplastic syndromes—21% experience recurrence or new PNS post-thymectomy.