Trismus as the Initial Presentation of Anti-Hu Paraneoplastic Neurological Syndrome.

A 73-year-old man presented with subacute trismus and pancerebellar dysfunction. Brain imaging and routine blood test results were unremarkable. Chest computed tomography revealed an indistinctly enhancing 4.7 × 2.5 × 1.8-cm³ pulmonary mass in the right upper lung, with enlarged right paratracheal and hilar lymph nodes. Biopsy of the right supraclavicular lymph node confirmed metastatic carcinoma, with differential diagnoses of small cell carcinoma and poorly differentiated carcinoma, indicating lung cancer as the primary source. Paraneoplastic immunohistochemistry screening revealed anti-Hu antibodies in the serum at a titer of 1:7680 (normal range <1:240) and in the cerebrospinal fluid (CSF) at a titer of 1:256 (normal range <1:2). The line blot method yielded positive results for anti-Zic4 antibodies in serum, with a titer of >1:10 (normal range <1:10), whereas CSF anti-Zic4 was negative (normal range <1:2). The patient developed non-responsive hospital-acquired pneumonia and respiratory failure, and discharged himself against medical advice. This rare case indicates that trismus can be an initial manifestation of anti-Hu paraneoplastic neurological syndrome, and emphasizes the importance of clinical awareness.