小纖維神經病變之臨床、病理及生理之研究

Abstract

周邊神經是由直徑大小不等的各種神經纖維所組成。小纖維神經病變(small-fiber neuropathy)是神經病變的一種亞型的，是指在解剖上或是生理上主要侵犯小纖維神經或影響其生理功能之神經病變，被侵犯的可以是體神經或自律神經或兩者。在周邊神經病變中，小纖維神經病變常佔了重要的成分，也是造成病人臨床症狀的主因之一，其中包括擾人的神經痛，不僅給病人帶來不舒服感，影響其生活品質，還會對社會經濟造成嚴重的負擔，由於傳統的神經傳導檢查對於小纖維神經病變缺乏診斷力，因此過去小纖維神經病變一直是神經醫學診斷、研究的盲點，其治療也多為經驗性。皮膚切片評估末梢神經病變是一項新的成熟的病理診斷工具，接觸性熱刺激誘發電位 (contact heat evoked potential)則是一項具有潛力的檢查可以用來探討小纖維感覺神經之病態生理變化。本研究希望藉由皮膚切片及接觸性熱刺激誘發電位探討小纖維神經病變之病理及生理致病機轉及其臨床上重要性。 第一部分的研究目標旨在釐清於小纖維神經病變當中，表皮內神經退化臨床上的危險因子及其對感覺異常、神經痛及自律神經功能異常所扮演的角色。研究對象選定(1) 嗜酸性白血球增生症的病患及 (2) 慢性腎病變之患者。我們收集12例嗜酸性白血球增多症併發神經病變之病患（8位男性及4位女性，年齡為 47.9 ± 11.7歲;範圍為 27〜71歲）。其中6位患者是Churg-Strauss 症候群，另外6例是原發性。所有12例都表現急性或亞急性的多發性單一神經病變或是多發性神經病變。患者最初的神經學症狀都是感覺異常。與正常對照組相較，表皮內神經纖維密度在嗜酸性白血球增多症之病患顯著降低（2.12 ± 2.30 vs 10.56 ± 3.69纖維 /毫米，p值= 0.0001）。其中有10例 (83.3%)表皮內神經纖維密度為異常。表皮內神經纖維密度與病患當時之失能程度呈負相關（p = 0.003）。此外，在所有的Churg-Strauss症候群患者和3例原發性患者中可以見到皮膚切片中表現出血管炎病理現象，其中6例皮膚血管炎病灶顯示血管周圍嗜酸性白血球浸潤（圖I-1A）。另外我們收集有40例慢性腎臟病之病患（14名女性和26名男性），年齡為 60.7 ± 12.3（範圍，33〜79歲），包括2例第3期，6例第4期及32例末期慢性腎臟病。平均腎臟病持續時間為 7.1 ±7.3 年（0.3〜35年）。共有21位患者 (52.5%) 有神經學症狀，包括感覺症狀或自主功能障礙，慢性腎臟病病患表皮內神經密度均顯著低於對照組（2.81 ± 1.95 vs 8.58 ± 2.84纖維 / 毫米，p = 0.0001）。有27位（67.5％）患者表皮內神經密度為異常，15例（37.5％）有神經傳導檢查的異常，29例（72.5％）有異常的自主神經功能檢查結果。在多元線性回歸模型分析下，表皮神經的密度仍與腎臟疾病持續時間呈負相關（p = 0.02）而與高密度脂蛋白膽固醇呈正相關 (p值= 0.018)。另外，表皮內神經密度與休息時RR間期變異（p = 0.009）及腳底交感神經皮膚反應（p = 0.039）也呈現關聯性。 在第一部分研究中，我們驗證了皮膚切片在評估小纖維神經病變之可行性，也驗證了小纖維神經病變的確是某些系統性疾病如腎臟病的主要併發症之ㄧ，是造成感覺及自律功能失調症狀之重要原因。皮膚切片可以表現血管炎病理變化，顯示皮膚切片還可以反映神經破壞的病理機制。 第二部分的研究目標旨在研究及開發小纖維神經之神經生理檢查。接觸性熱刺激誘發電位是一項新的技術可以偵測小纖維感覺神經活化後所產生的大腦電器活動，代表的是小纖維感覺神經所引發的生理反應。首先我們收集了70位正常人，33名男性（40.9 ± 13.8歲，範圍 22-67歲）和37名女性（38.3 ± 10.5歲，範圍 24-62歲）。攝氏51度的接觸性熱刺激可以在所有的正常人誘發出典型先負後正的雙向波形。上肢及下肢N波潛時分別為398.63±28.55及449.03±32.21毫秒，P波潛時為541.63±37.92 及595.41±39.24毫秒，N–P波振幅分別為42.30±12.57及39.67±12.03微伏特。在多元線性回歸模型分析下，N–P波振幅與年齡呈負相關，上下肢N波潛時則與性別有相關性，女性的潛時較短。另外熱刺激產生疼痛知覺的強度評分與年齡呈負相關且女性高於男性。該評分也與N波潛時呈負相關而和N-P波振幅呈正向線性相關。這結果顯示接觸性熱刺激誘發電位可以反映疼痛知覺，疼痛越強，則N-P波振幅越高而N波潛時越短。之後我們將接觸性熱刺激誘發電位應用於32例第2型糖尿病併神經痛的病患（男20例，女12例）。所有病患都有表皮內神經密度異常的情形。表皮內神經密度平均為1.1 ± 1.5纖維/毫米（範圍是 0〜5.7纖維/毫米）。與正常對照組相較，患者N-P波振幅明顯下降（14.8 ± 15.6 vs 33.7 ± 10.1 μV， p < 0.001），有26例（81.3％）接觸性熱刺激誘發電位的參數是異常的。在多元線性回歸模型分析下，接觸性熱刺激誘發電位的振幅與表皮內神經密度（p = 0.003）及疼痛知覺的強度評分（p = 0.019）呈現正相關。另外，我們定義熱刺激誘發電位的N-P波振幅與表皮內神經密度的比值為”興奮指標”，它反應的是大腦對熱刺激的反應 (大腦輸出) 與表皮內神經密度(周邊輸入) 相對應之變化。結果顯示第2型糖尿病神經病變併神經性疼痛的病患之”興奮指數”顯著高於正常對照組（44.03 ± 97.31 vs 3.95 ± 1.02; p = 0.023）。我們也發現有誘發性疼痛（evoked pain）之特徵的病患，熱刺激誘發電位的振幅比那些沒有該項症狀的患者為高（24.9 ± 14.8 vs 10.2 ± 14 μV的，p = 0.011）；但是表皮內神經密度在這兩群病患之間並無差異 (1.1 ± 1.1 vs 1.1 ± 1.6纖維 / 毫米，p = 0.989）。這些研究結果顯示接觸性熱刺激誘發電位波形在正常人身上的穩定性，可做為臨床之應用，接觸性熱刺激誘發電位振幅和潛時分別受到年紀與性別的影響，而且可以反應疼痛知覺的強度。在小纖維神經病變時，電位的振幅明顯下降且潛時明顯延長。表皮內神經密度是決定接觸性熱刺激誘發電位的振幅最重要的因子。另外，我們也發現接觸性熱刺激誘發電位可以反映誘發性疼痛之病生理變化及大腦對熱刺激的活性在神經痛的患者相對是增的。

Small-fiber nerves, including thinly myelinated Aδ and unmyelinated C fibers, are major components of peripheral nerves and are affected by a variety of diseases including infection, autoimmune, metabolic, toxin, and malignancy. Small-fiber neuropathy presents with various patterns of sensory disturbance and autonomic dysfunction. Neuropathic pain is common in small-fiber neuropathy, often causes great troublesome to patients, and is a challenge for neurologists. Conventional electrophysiological study is insensitive to small-fiber nerve dysfunction. Skin biopsy with quantification of intraepidermal nerve fibers (IENF) is well-developed pathological method to study small-fiber sensory nerves. Contact heat evoked potential (CHEP) is a new technique to investigate cerebral responses to thermal stimuli mediated by Aδ-fibers. We aimed to investigate the pathological-physiological mechanism and clinical consequences of small-fiber neuropathy. The first portion of my study is to clarify the associated factors and the clinical significance of small-fiber neuropathy in two type of disease: eosinophilia-associated neuropathy and chronic kidney diseases (CKD). We included twelve patients with neuropathy and concomitant eosinophilia. Six patients fulfilled the criteria of Churg-Strauss syndrome and the other 6 were categorized as primary eosinophilia. All 12 patients had mononeuropathy multiplex or polyneuropathy with sensory symptoms as the initial manifestation. IENF densities were reduced in 10 patients (83.3%), being significantly lower than the controls (2.12 ± 2.30 vs. 10.56 ± 3.69 fibers/mm, p = 0.0001) and negatively correlated with the disability grade (p = 0.003). Nine patients (75%), including all 6 patients with Churg-Strauss syndrome, had cutaneous vasculitis, and two-thirds of these patients had perivascular infiltration of eosinophils. We also applied skin biopsies, autonomic function tests, and nerve conduction studies (NCS) to investigate the spectrum of neuropathies in 40 consecutive non-diabetic patients with late-stage CKD (14 females and 26 males, aged 60.73 ± 12.27 years), including 2 cases with stage 3 CKD, 6 with stage 4 CKD, and 32 with stage 5 CKD, i.e., end-stage kidney disease. Clinically 21 patients (52.5%) were symptomatic with paresthesia over the limbs or autonomic symptoms. The IENF density was markedly reduced in CKD patients compared to age- and gender-matched controls (2.81 ± 1.95 versus 8.58 ± 2.84 fibers/mm, p < 0.0001). Skin denervation was observed in 27 patients (67.5%). Fifteen patients (37.5%) had abnormalities on NCS, and 29 patients (72.5%) had abnormal results on autonomic function tests. By analysis with multiple regression models, the IENF density was negatively correlated with the duration of renal disease (p = 0.02) and positively correlated with the serum level of high-density lipoprotein-cholesterol (HDL-C, p = 0.018). Additionally the R-R interval variability at rest was linearly correlated with the IENF density (p = 0.02) and the absence of sympathetic skin responses at the soles was associated with reduced IENF density (p = 0.031). Taken together, skin biopsies provide an approach to investigate systemic influences on small-fiber sensory nerves and the cutaneous vasculature. Small-fiber sensory and autonomic neuropathies constitute the major form of neuropathy in late-stage CKD, and skin denervation was associated with the duration of renal disease and lower levels of serum HDL-C. The aim of secondary portion of my study is to investigate the physiology of small-fiber nerves by contact heat evoked potentials. First we applied contact heat evoked potentials (CHEP) to investigate the cerebral responses to thermal stimuli in 70 healthy subjects (33 men and 37 women, 39.56 ± 12.12 years). With heat stimulation of fixed-intensity (51 °C) on the distal forearm and distal leg, CHEP revealed consistent waveforms with an initial negative peak (N latency: 398.63 ± 28.55 and 449.03 ± 32.21 ms for upper and lower limbs) and a later positive peak (P latency: 541.63 ± 37.92 and 595.41 ± 39.24 ms for upper and lower limbs) with N-P interpeak amplitude of 42.30 ± 12.57 μV in the upper limb and 39.67 ± 12.03 μV in the lower limb. On analyses with models of multiple linear regression, N-P amplitudes were negatively correlated with age and N latencies were correlated with gender, with females having shorter latencies. The verbal rating scale (VRS) for pain perception was higher in females than males, and decreased with aging. Additionally, VRS paralleled changes in N-P amplitude and N latency; the higher the VRS, the shorter was N latency and the higher was N-P amplitude. Secondly we investigated the diagnostic role of CHEP in small-fiber neuropathy. There were 32 type 2 diabetic patients (20 males and 12 females, aged 51.63±10.93 years) with skin denervation and neuropathic pain. CHEP amplitude was reduced in patients compared to age- and gender-matched controls (14.8±15.6 vs 33.7±10.1 μV, p<0.001). Abnormal CHEP patterns (reduced amplitude or prolonged latency) were noted in 81.3% of these patients. The CHEP amplitude was the most significant parameter correlated with IENF density (p=0.003) and pain perception to contact heat stimuli (p=0.019) on multiple linear regression models. An excitability index was derived by calculating the ratio of the CHEP amplitude over the IENF density. This excitability index was higher in diabetic patients compared to controls (p=0.023), indicating enhanced brain activities in neuropathic pain. Among different neuropathic pain symptoms, the subgroup with evoked pain had higher CHEP amplitudes than the subgroup without evoked pain (p=0.011). In summary, these findings suggest the consistence and applicability of CHEP in clinical practice to study the physiology of small-fiber sensory nerves. CHEP is significantly influenced by aging and gender, and is corresponding to the thermal pain perception. CHEP offers a noninvasive approach to evaluate the degeneration of thermonociceptive nerves in small-fiber neuropathy by providing physiological correlates of skin denervation and neuropathic pain.