Hypokalemic periodic paralysis induced by thymic hyperplasia and relieved by thymectomy.
OBJECTIVE
Hypokalemic periodic paralysis is a muscle channelopathy based on mutations or predisposing variants or secondary to potassium wasting. In contrast to myasthenia gravis, an association with thymic hyperplasia has not yet been reported, to our knowledge.


METHODS
We report a male patient in his mid-20s with progressive episodes of flaccid muscle weakness, associated low serum potassium levels, and a pathologic decrement in the long exercise test. Because the familial inheritance in the family was initially unknown, thorough diagnostic tests were performed including contrast-enhanced computed tomography scan, which displayed a mass in the anterior mediastinum. The test results for autoantibodies against myasthenia gravis (acetylcholine receptor, muscle-specific tyrosine kinase, and low-density lipoprotein receptor-related protein 4) and other end plate channelopathies were negative, and test results for hypokalemia-inducing hormones (thyroid, corticotropin, and cortisol) were negative. Surgery identified a thymus of 13 × 8 × 3 cm(3). Histologic analysis was consistent with thymic hyperplasia of the follicular subtype and immunohistologic analysis showed cytokeratin 5/6 in hyperplastic epithelial cells. A 2-year follow-up revealed the postoperative absence of weakness episodes. As in 30% of familial cases, molecular genetics testing failed to identify a mutation in periodic paralysis genes.


CONCLUSIONS
Thymic hyperplasia can clinically manifest susceptibility to hypokalemic periodic paralysis. For patients with late onset or increasing weakness episodes, we recommend imaging to assess for thymic enlargement and thymectomy at thymic hyperplasia.
Department of Thoracic Surgery, 117 PLA Hospital, Hangzhou, China.
Renrong
R
Yang
Karin
K
Jurkat-Rott
Jinlin
J
Cao
Guofeng
G
Wang
Hans-Peter
HP
Seelig
Changping
C
Yang
Guibao
G
Liu
Lin
L
Pan
Haiyan
H
Zheng
Frank
F
Lehmann-Horn
D000324:Adrenocorticotropic Hormone / Q000378:metabolism; D000328:Adult; D015703:Antigens, CD; D005080:Exercise Test; D005500:Follow-Up Studies; D006801:Humans; D020514:Hypokalemic Periodic Paralysis / Q000175:diagnosis / Q000209:etiology* / Q000601:surgery*; D008279:Magnetic Resonance Imaging; D008297:Male; D013934:Thymectomy / Q000379:methods*; D013950:Thymus Gland / Q000473:pathology; D013952:Thymus Hyperplasia / Q000150:complications*; D014057:Tomography, X-Ray Computed
D015703:Antigens, CD; D000324:Adrenocorticotropic Hormone