Capillaroscopy – Role in Modern Rheumatology

Introduction:

Capillaroscopy is a non-invasive, safe, and essential diagnostic tool used in rheumatology to evaluate various conditions. In this technique, the small vessels involved in the microcirculation are evaluated, usually the vessels present in the nail fold. This helps evaluate the general architecture of capillary rows and the details of the respective vessels. One of the main goals of capillaroscopy is in the differential diagnosis of primary and secondary Raynaud’s phenomenon and the diagnosis of scleroderma spectrum disorders.

What Is Capillaroscopy?

Capillaroscopy is an in vivo technique in which optical magnification is used to study the microcirculation of capillaries. This technique can be carried out at any anatomical location where terminal capillaries are in a parallel direction to the skin, such as in the labial mucosa, ocular conjunctiva, and periareolar region. But the capillaries of nail folds of the hands are most commonly accessed with this technique, as the capillaries are parallel to the skin at various locations.

These are usually perpendicular, and therefore this method is also called nail fold capillaroscopy. For this procedure, different optical instruments can be used, which allows the dynamic assessment of the microvascular abnormalities and the computerized study of different capillary parameters. The magnification usually depends upon the type of device used, but the lenses can range from a low magnification of 20x up to a high magnification of 1000x.

What Is the History of Capillaroscopy?

The nail fold capillaries were first observed in the 17th century, during which primitive magnifying instruments were used. Later during the 19th century, the association between inflammation and capillaries was discovered.

Maurice Raynaud was the first to find a direct connection between capillary abnormalities and certain medical conditions in the second half of the 19th century. However, in the 1930s, the interest in capillaroscopy declined. Later in the 21st century the interest revived again with the advent of modern equipment that can be visualized easily.

What Is the Principle of Capillaroscopy?

The principle of capillaroscopy depends upon the microcirculation in the capillaries. The capillaries are found throughout the skin however they run perpendicular to the skin surface, and only the capillaries in the nail fold are present parallel to the skin. Therefore, all the morphological details and nature of blood flow can be easily studied.

• The primary function of microcirculation is a capillary exchange which means the delivery of oxygen and nutrients to the body tissues and removing carbon dioxide and waste products from the body.

• The vasculature of the microcirculation consists of the smallest blood vessels present in the human body, including arterioles, capillaries, and venules.

• The capillaries are formed by an arterial limb, capillary loop, and venous limb. This pattern is seen within every tissue except in the liver, spleen, and bone marrow, where sinusoids are present instead of capillaries.

• With the help of different instruments, the column of blood can be easily visualized within these capillaries.

• In patients with systemic diseases, vascular damage and abnormality in capillary morphology can be observed well before symptoms onset, which helps identify patients with rheumatic diseases.

What Are the Indications for Capillaroscopy?

The capillaroscopy can be done to identify the following conditions:

• Differential diagnosis of primary and secondary Raynaud’s phenomenon (a condition causing decreased blood flow in fingers).

• Staging of systemic sclerosis (a rare condition causing tightening or hardening of the skin).

• Differential diagnosis of dermatomyositis (an inflammatory condition causing muscle weakness and skin rashes) and polymyositis (an inflammatory condition of muscle weakness).

• Differential diagnosis of interstitial lung disease (group of diseases causing scarring of lung tissues).

• Predicting the formation of new digital ulcers in systemic sclerosis.

• Response assessment of dermatomyositis treatment.

What Instruments Are Used in Capillaroscopy?

The different types of instruments that can be used in capillaroscopy include:

• Wide-Field Stereo Microscope - This optional magnifying equipment helps magnify the capillaries upto 20x so that they can be easily visualized. It provides a panoramic view of nail fold capillaries and helps in evaluating them. However, this instrument is very expensive and non-portable.

• Ophthalmoscope and Dermatoscope - These portable instruments provide images with lower magnification and quality. They are mostly used as bedside evaluation tools by clinicians. They are not expensive as compared to stereo microscopes, but they do need image storing and processing capabilities.

• Microscope - An optical microscope and digital video camera are usually connected to a computer. These can be used in varying magnifications ranging from 200x to 600x. Moreover, these are cost-effective instruments and easily available, therefore best suited for outpatient settings.

• Nail Fold Videocapillaroscopy (NFVC) - This method provides high magnification of 200x to 600x and uses specific software that allows precise measurements of capillaries, including capillary length, width, and density. The only disadvantage of this equipment is its high cost.

What Is the Procedure of Capillaroscopy?

Any of the equipment mentioned above can be used to visualize capillaries. The steps involved in this procedure are:

• The skin of the finger that has to be examined is first cleansed with soap and water.

• After that, a drop of immersion oil, such as cedarwood oil, olive oil, and peanut oil, can be applied to the skin of the nail fold to enhance skin transparency.

• In the routine examination, all the nail folds of the fingers can be examined except the thumbs.

• Each finger should be examined under two magnifications, such as 50x and 200x to 300x. A series of 4 to 12 overlapping images are taken of each finger in which the morphological details and all parameters of capillaries can be examined.

• The fingers that have sustained any injuries are avoided, and usually, the fourth and fifth fingers are examined as they have very transparent skin, which is easy to examine.

What Are the Important Parameters of Capillaries?

• Skin Transparency and Visibility- Transparent so that capillaries are easily visible.

• Capillary Architecture- Straight capillaries parallel to the nail fold.

• Capillary Morphology- U-shaped.

• Capillary Loop Diameter- < 20 µm (micrometer).

• Capillary Density- 9 to 13 in 1 linear millimeter.

• Capillary Blood Flow- Normal, without any stasis or thrombosis.

• Avascular Areas - When the distance between 2 loops is greater than 500 µm are absent.

• Hemorrhages- Usually absent, may be present after local trauma.

• Neoangiogenesis- Absent.

• Dilated (20 to 50 µm) and Giant (> 50 µm) Loops- Absent.

• Pericapillary Edema- Absent.

What Is the Use of Capillaroscopy in Rheumatic Diseases?

In complaints such as arthralgia, Raynaud’s, and lung disease conditions, the patients lack clinical features which help diagnose systemic connective tissue diseases such as scleroderma. In such cases, capillaroscopy is crucial in identifying whether the disease is a connective tissue disease.

1. Raynaud’s Phenomenon - This phenomenon is an exaggerated vasculature response to cold and other stimuli. It can be either primary (in the absence of associated disorders) or secondary (associated with systemic diseases). Therefore, capillaroscopy helps in distinguishing between primary and secondary Raynaud’s.

2. Systemic Sclerosis - In systemic sclerosis, three types of capillaroscopy patterns can be seen, which include early, active, and late.

• Systemic Sclerosis - Early Pattern - In this, few giant capillaries, few hemorrhages with well-preserved capillary distribution, and no evident loss of capillaries can be seen.

• Systemic Sclerosis - Active Pattern - In this, frequent giant capillaries and hemorrhages, loss of capillaries, and mild disorganization of the capillary architecture can be seen.

• Systemic Sclerosis - Late Pattern - In late pattern, irregular enlargement of capillaries with few giant capillaries and hemorrhages can be seen. A large amount of loss of capillaries can be seen with avascular areas and disorganization of capillaries structure.

Conclusion:

Capillaroscopy is an easy, safe, and minimally invasive method that helps diagnose peripheral microcirculation pathologies. This digital technology capillaroscopy helps in evaluating the precise qualitative and quantitative evaluation of the microcirculation and is used as a routine diagnostic tool by various rheumatologists.