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A Case of Muscle Twitching With Psoriasis

Educational Objective
Based on this clinical scenario and the accompanying image, understand how to arrive at a correct diagnosis.
1 Credit CME

A 42-year-old man presented with a 2-month history of persistent muscle twitching in his abdomen and bilateral calves during wakefulness and sleep accompanied with excessive sweating, as well as mild bilateral lower extremity weakness after prolonged walking. The patient denied confusion, memory problems, hallucinations, and sleep disturbance. He had psoriasis for 30 years, for which he was taking steroids intermittently, and hypothyroidism for 4 years, for which he was taking levothyroxine. His family history was unremarkable. His examination results were significant for psoriatic skin lesions and purple stria in the abdomen and both calves. Undulating wavelike movements were visible on the muscle surface of the abdomen and calves (Video). The remaining general and neurological examination results were normal. Laboratory test results, including creatine kinase, thyrotropin, antinuclear antibodies, paraneoplastic antibodies (includes Hu, Yo, Ri, CV2, Ma2, and amphiphysin antibodies), were normal. Chest computed tomography results were normal.

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A. Autoimmune Isaacs syndrome

Nerve conduction study results were normal except for the presence of an M-wave (Figure 1) after discharges in posterior tibialis nerve (prolonged after-discharges in an F-wave of posterior tibial nerve). Needle electromyography (EMG) results showed frequent fasciculations, doublets, triplets, and multiple myokymic discharges (Figure 2) in several muscles of the upper and lower extremities in addition to the abdomen (biceps, gastrocnemius, first interosseous muscle, and rectus abdominis). The voluntary activation results were normal. These features are consistent with a diagnosis of neuromyotonia. Indirect immunofluorescence staining of HEK293 transfected cells showed positive voltage-gated potassium channel (VGKC)–complex antibodies, with contactin-associated protein-like 2 antibodies (CASPR2-Ab) titer at 1:100 and leucine-rich glioma inactivated protein 1 antibodies (LGI1-Ab) titer at 1:10. A diagnosis of autoimmune Isaacs syndrome was made. Mycophenolate mofetil, 1000 mg twice daily, and a tapering dose of prednisone, 60 mg, were prescribed. At the 3-month follow-up, his muscle twitching and skin lesion had subsided. Repeated serum CASPR2-Ab and LGI1-Ab results were negative.

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Article Information

Corresponding Author: Hongzhi Guan, MD, Department of Neurology, Peking Union Medical College Hospital, No. 1 Shuaifuyuan, Wangfujing, Beijing, 100730 China (guanhz@263.net).

Published Online: July 15, 2019. doi:10.1001/jamaneurol.2019.1937

Conflict of Interest Disclosures: None reported.

Additional Contributions: We thank Haitao Ren, Peking Union Medical College Hospital, for assisting with antibodies testing and Shougang Guo and Shanshan Gao, Shandong Provincial Hospital (affiliated with Shandong University), for performing electromyograms and nerve conduction studies. These individuals were not compensated for their contributions.

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