非外傷性後骨間神経麻痺に対する超音波検査の意義

Clinical Significance of Ultrasonography for the Diagnosis of Nontraumatic Posterior Interosseous Nerve Palsy

要旨　目的：後骨間神経（PIN）の非外傷性麻痺の原因には，占拠性病変（主にガングリオン），PINのくびれ，絞扼（回外筋症候群）がある．今回，原因の同定に超音波検査（US）を行い有用性を評価した．方法：本麻痺の7例7肘を対象とした．PINと周囲組織をUSにより観察した．結果：以下のUS所見により3原因を同定できた．1）占拠性病変（2肘）：いずれも低エコーでガングリオンと診断した．PINはこれにより挙上され，Frohse腱弓で圧迫されていた．2）PINのくびれと全長性の腫大（3肘）．3）Frohse腱弓下でのPIN径の減少と近位の腫大（仮性神経腫）（2肘）：回外筋症候群と診断した．結論：USは非外傷性PIN麻痺の原因検索に有用である．

Abstract　Objective : Causes of nontraumatic posterior interosseous nerve (PIN) palsy include space-occupying lesions, constrictions of the PIN, and supinator syndrome. The purpose of this study was to identify these causes using Ultrasonography (US). Methods : We performed US in seven cases (seven elbows) with palsy and examined the PIN and surrounding structures. Results : We identified the three causes by the following US findings : 1) A space-occupying lesion in two elbows. Both were low-echoic and diagnosed as ganglion. In these two cases, the PIN was elevated by the lesion and compressed against the arcade of Frohse. 2) A diffusely swollen PIN with constrictions was found in three cases. 3) A PIN showing a reduction in caliber beneath and a swelling (pseudoneuroma) proximal to the arcade of Frohse, compatible with supinator syndrome was also identified. Conclusion : US is useful for the diagnosis of nontraumatic PIN palsy.