**6. Utility of capillary microscopy in rheumatology**

Rheumatologists frequently encounter situations in which patients present with complaints such as arthralgia, Raynaud's, lung disease, etc. However, many of these patients lack the typical clinical features to classify as a definite systemic connective tissue disease such as scleroderma, MCTD, and others. In such scenarios, NFC can serve as a useful modality in differentiating patients with and without connective tissue disease. The common nail abnormalities encountered include dilated loops, microhemorrhages, and capillary dropouts. Here we shall study the NFC abnormalities encountered in patients with rheumatological diseases.

#### **6.1 Raynaud's phenomenon**

Raynaud's phenomenon is an exaggerated responsiveness of the vasculature to cold and other stimuli. It can be primary (in absence of an associated disorder) or secondary (associated with a systemic disease such as scleroderma). NFC can serve as a useful tool in distinguishing primary from secondary Raynaud's. Mannarino et al. [10] described three capillaroscopic patterns in patient with

Raynaud's—normal, borderline, and abnormal patterns. Authors proposed the borderline NFC abnormalities (composed of shorter and more tortuous capillaries) are due to the long-standing vasospastic reaction of the Raynaud's itself. Of interest though is the finding of abnormal capillaroscopic pattern in 8/44 patients with idiopathic Raynaud's phenomenon. These are the group of patients who might be at a higher risk for developing connective tissue disease on follow-up. On the other hand, the absence of NFC abnormalities in a patient of Raynaud's is also helpful in the exclusion of scleroderma [11].
