Liệt chu kỳ (Hypokalaemic periodic paralysis)

Mô tả: Periodic paralysis presents as episodes of painless muscle weakness that are often sudden and associated with preserved consciousness. Proximal muscles are affected more than distal muscles, and reflexes are decreased or absent. Periodic paralysis is associated with hypokalaemia.

Nguyên nhân: • Hyperthyroidism • Congenital – most forms

Cơ chế: Defects in muscle ion channels are the key cause of thyrotoxic periodic paralysis, although the how or why is unclear.72 Hyperthyroidism increases the activity of the Na+K+ pumps on muscle cells, producing a large and rapid shift of potassium intracellularly and leading to hyperpolarisation and absent muscle cell depolarisation.

Ý nghĩa lâm sàng: It is a rare event affecting between 2% and 20%, and 0.1% and 0.2%, in Asian and American populations, respectively. There is no correlation between severity of hyperthyroidism and the manifestation of paralysis.73