認識乾癬性關節炎

　　乾癬性關節炎是一種自體免疫病所引起的關節病，表現為皮疹、關節腫痛、僵硬和運動障礙。關節炎最好發在指(趾)的遠端指關節，典型特徵是臘腸樣指(sausage- shaped digits)。 　　乾癬性關節炎(Psoriatic arthritis，PsA)是一種與乾癬(psoriasis)相關的炎症性關節病，表現為皮疹、關節腫痛、僵硬和運動障礙，可合併出現骶髂關節炎(sacroiliitis)或脊椎炎(spondylitis)，晚期可出現關節強直。任何年齡皆可發生，以30~50歲最多見，男女無明顯差異，但其中脊椎受侵犯以男性居多。

　　具體病因仍不清楚，可能與感染(infection)、外傷(trauma)、異常的細胞免疫與體液免疫(cellular immunity 及 humoral immunity)功能異常有關。 　　病理機轉和RA相同，包括：

1. synoviocytic hyperplasia：但乾癬性關節炎的Synovium是more vascular，且很少有巨噬細胞聚集，以及內皮白細胞黏附分子-1表達較少(fewer macrophages and less expression of endothelial cell leukocyte adhesion molecule-1 (ELAM-1))；
2. 早期多核巨嗜白血球浸潤，稍後單核白血球(early PMN infiltration and later mononuclear cell infiltration)；
3. 軟骨破壞與血管翳的生成(cartilage erosion, and pannus formation)；

　　多數患者起病無明顯誘因，緩慢發病，只有少數可以有關節外傷史，乾癬可能在關節炎出現前數年便發生。有許多患者主訴晨僵(morning stiffness)。關節炎最喜愛發生在手指或腳趾的遠端或近端指關節(PIP orDIP joints)，典型特徵是臘腸樣指(sausage- shaped digits)，其餘部位如knees、hip、wrists、ankles較少發生。有1/3患者可出現inflammatory ocular complications，如結膜炎、紅膜炎、鞏膜炎(conjunctivitis, iritis, episcleritis)。1/3出現胃腸道炎。常見關節表現如下：

單一或多關節腫痛、僵硬(Pain, swelling, red or warm to the touch ,or stiffness in one or more joints)

遠端和近端指(趾)間關節滑膜炎和腱鞘炎，會造成整隻手指或腳趾嚴重的腫脹，呈現臘腸指(趾)(Sausage-like swelling in the fingers or toes, known as dactylitis)

足跟痛是起止點炎的表現，就是在腳底、腳跟等肌腱、韌帶與骨頭相連處炎症(Pain in and around the feet and ankles, especially tendinitis in the Achilles tendon or Plantar fasciitis in the sole of the foot)

指(趾)甲病變，如頂針樣凹陷或指甲脫離(Changes to the nails, such as pitting or separation from the nail bed)、角化過度、增厚、橫脊及變色。幾乎所有患者有指甲萎縮(onychodystrophy)，藉此可以和RA區分

骶髂關節炎之下背痛Pain in the area of the Sacrum (the lower back)

　　依據臨床特點，關節炎分為五種類型(There are five main types of psoriatic arthritis)：

單關節炎或非對稱型 (占 70%) (Asymmetric)	病變以 DIP 為主，輕微(mild)不對稱分布，一般少於 3 的關節。因伴發滑膜炎和腱鞘炎，所以受損指 ( 趾 ) 可呈現“臘腸樣指病變”；另外，常伴有指甲病變(This type does not occur in the same joints on both sides of the body and usually only involves fewer than 3 joints)
對稱性多關節炎型 (占 15%) (Symmetric)	病變以 PIP 為主，可累及 DIP 及大關節，如 wrist,elbow,knee 和 ankle 等關節，與 RA 相似(This type affects joints on both sides of the body simultaneously. This type is most similar to rheumatoid arthritis and is disabling in around 50% of all cases)
破壞關節型 (占 5%) (Arthritis mutilans)	嚴重型，好發於 20-30 歲，指骨、掌骨、蹠骨可有骨溶解；指節常有望遠鏡式套疊現象；關節可僵直、畸形，常伴發熱和骶髂關節炎，皮損嚴重，為膿皰型(Arthritis mutilans has also been called chronic absorptive arthritis)
遠端指間關節型 (占 5%) (Distal interphalangeal predominant)	病變在遠端指間關節，通常與乾癬指甲病變相關(This type is characterised by inflammation and stiffness in the joints nearest to the ends of the fingers and toes. Nail changes are often marked)
脊柱病型 5% (Spondylitis)	以單側脊柱和骶髂關節病變為主，也可侵犯手腳關節；下背痛或胸壁痛症狀輕微，韌帶骨贅形成，嚴重時脊柱融合、關節間隙狹窄甚至融合；可影響頸椎，導致寰椎半脫位(This type is characterised by stiffness of the spine or neck, but can also affect the hands and feet, in a similar fashion to symmetric arthritis)

1. 血液檢查異常很少見，炎症活動時，ESR、CRP和complement↑；RF多數陰性，但對稱性多關節炎型(symmetric arthritis)可能會升高；IgA、IgE可能升高；可能ANA陽性; 半數患者HLAB27(+)，且與骶髂關節和脊柱受侵犯顯著相關。
2. 影像學檢查

   周圍關節炎

   骨質有破壞(erosions)和增生(proliferation of bone)表現：軟組織腫脹(soft tissue swelling)、手指強僵直(bony ankylosis of fingers)、指間關節間隙變窄(loss of the cartilage space)；近端指骨變尖和遠端指骨增生，造成筆帽樣畸形(tapering of the proximal phalanx and cuplike erosions and bony proliferation of the distal terminal phalanx ("pencil-in-cup" appearance))；指節常有望遠鏡式的“套疊”現象(telescoping of one bone into its neighbor, leading to the "opera-glass" deformity)

   中軸關節炎

   多表現為單側骶髂關節炎(sacroiliitis)：關節間隙變窄或融合、韌帶骨贅形成(nonmarginal syndesmophytes)，椎旁骨化(paravertebral ossification)，形成骨橋

　　以下幾點有助於乾癬性關節炎的診斷(Factors that contribute to a diagnosis of psoriatic arthritis)：

病史及家族史	Psoriasis in the patient, or a family history of psoriasis or psoriatic arthritis
RF	A negative test result
關節炎表現	Arthritis symptoms in the distal Interphalangeal articulations of hand (the joints closest to the tips of the fingers)；inflammation in the Achilles tendon，the Plantar fascia
指甲	Ridging or pitting of fingernails or toenails (onycholysis)
影像學檢查	Radiologic images indicating joint change：如sausage- like swelling of the fingers or toes(dactylitis)

乾癬性關節炎、自體免疫病、關節病、臘腸樣指、運動障礙、脊椎炎、臨床醫學資訊館