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Functional (psychogenic) limb weakness describes genuinely experienced limb power or paralysis in the absence of neurologic disease. The hallmark of functional limb weakness is the presence of internal inconsistency revealing a pattern of symptoms governed by abnormally focused attention. In this chapter we review the history and epidemiology of this clinical presentation as well as its subjective experience highlighting the detailed descriptions of authors at the end of the 19th and early 20th century. We discuss the relevance that physiological triggers such as injury and migraine and psychophysiological events such as panic and dissociation have to understanding of mechanism and treatment. We review many different positive diagnostic features, their basis in neurophysiological testing and present data on sensitivity and specificity. Diagnostic bedside tests with the most evidence are Hoover's sign, the hip abductor sign, drift without pronation, dragging gait, give way weakness and co-contraction., (© 2016 Elsevier B.V. All rights reserved.)

Objective: We aimed to review the English and Chinese literature on Pa Ping and to confirm by personal interview the story of how its pathogenesis was uncovered., Background: In 1930, Dr. Alexander Stewart Allen noticed a pattern of illness arising in the region of Kiating, China. Area residents began presenting to local hospitals with nausea, vomiting, and diarrhea, and what emerged was a clinical picture of a gradual ascending paralysis that could result in death, termed Pa Ping. All 3 patients observed by Dr. Allen were male, had no family history of the disease, and had recently eaten before the onset of paralysis. Pa Ping developed in Dr. Allen himself, but he survived., Methods: Medical literature was reviewed for primary sources. Interviews of living descendants and friends of the doctors in China and North America were conducted and information was corroborated by written records., Results: Dr. Huang, with the National Central University College of Medicine, noticed a striking similarity between Pa Ping and familial periodic paralysis in 12 patients and reported 2 patients with Pa Ping treated with potassium citrate who experienced a reversal of the paralysis. Dr. K.T. Du analyzed meals of patients with Pa Ping seen by Dr. Zhe Tung and found barium in concentrations as high as 25.7%. This finding was confirmed by administering barium chloride to animals, which recapitulated the human syndrome., Conclusions: Although Dr. Huang had correctly noticed an underlying potassium depletion in patients with Pa Ping, the observations of Dr. Zhe Tung and Dr. K.T. Du ultimately established barium-induced hypokalemia as the underlying cause.