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Nailfold capillaroscopy is a rapid and easily applicable differential diagnostic technique that allows direct visualization of the microcirculation. Abnormal findings in nailfold capillaroscopy are closely associated with connective tissue diseases, such as systemic sclerosis. The clinical manifestation of impaired microcirculation is Raynaud's phenomenon, which is a classical symptom of connective tissue diseases. Nailfold capillaroscopy is increasingly used in various fields of medicine, therefore it is important to define methods for the acquisition and analysis of the results of nailfold capillary and to have a uniform definition of abnormal capillaries. This article discusses image acquisition and analysis, various capillaroscopic techniques, normal and abnormal capillaroscopic features and their significance, scoring systems and reliability of image acquisition and interpretation., (© 2022. The Author(s), under exclusive licence to Springer Medizin Verlag GmbH, ein Teil von Springer Nature.)

Competing Interests: Disclosure The authors report no conflicts of interest in this work.

The IgG4-associated diseases of connective tissue are caused by allergen-mediated autoimmune processes. The retroperitoneum, mesentery and mediastinum as well as other less common localizations, such as the neck, orbit and periarticular connective tissue can be affected. Inflammatory fibrosis is initially dominated by a lymphocytic and plasma cell-rich infiltrate and later by cell-poor storiform fibrosis. Stenosis and occlusion of vessels, ureters and intestines can cause severe complications. Computed tomography (CT) and magnetic resonance imaging (MRI) can be implemented in the diagnostic algorithm to narrow the differential diagnosis, delineate the distribution of fibrosis and reveal complications.

Systemic autoimmune diseases are responsible for about 25% of all deaths due to interstitial lung disease; therefore, an early identification of patients with pulmonary manifestation changes the management. Detection, differential diagnostic classification and staging of the pneumological pattern of findings are largely based on high-resolution computed tomography (HR-CT). The main differential diagnostic challenges are interstitial manifestations which present with radiological-histopathological phenotypes of interstitial pneumonia. The most common form of interstitial pulmonary reaction form of connective tissue diseases is the nonspecific interstitial pneumonia (NSIP) pattern. In rheumatoid arthritis, a usual interstitial pneumonia (UIP) pattern is dominant. Uncharacteristic reactions of airways and pleura can be the leading symptom or present as accompanying findings. A serious complication is pulmonary hypertension. Drug-induced lung lesions can present with similar HR-CT morphology as connective tissue diseases and can only be differentiated in the temporal and clinical context.

A 13-year-old girl presented with load-dependent pain of the medial part of the right foot. The medical history revealed no trauma and no sports-related injury. X-ray examinations of the foot and lower leg showed subcortical increased sclerosis at the medial part of the tibia, the medial tarsal bones and of a bunion. Magnetic resonance imaging revealed corresponding findings with localized edema of the bone marrow within the increased subcortical sclerosis but no indications of subcutaneous fibrosis. The constellation is indicative of melorheostosis, a rare benign sclerosis of bones and soft tissue. Subcutaneous fibrosis and limb shortening are also common.

Osteopoikilosis (Osteopathia condensans disseminata) is a rare and usually asymptomatic sclerosing bone dysplasia of unknown origin. Familial clustering suggests a dominant inheritance. The observation of a 47-year-old woman lead to differential diagnostic considerations in view of the literature on about 350 cases. For 2 years the patient has been complaining about pain and stiffness of both hands with swelling of the fingers. Additionally, she remarked about bilateral paresthesias corresponding to the sensory innervation of the median nerve. Clinical examination revealed a sensory carpal tunnel syndrome and mild synovitis of the proximal interphalangeal joints with skin induration and limited flexion of the fingers. In addition, some finger and toe nails showed pitting and most fingers had scar-like linear skin alterations. Radiologic findings showed symmetric, well-defined, homogeneous sclerosing areas in spongy bone. The combination of symmetrical sclerosing bone densities, hereditary character, and associated skin and joint manifestations suggests the existence of a general connective tissue disease.

During the last two decades, sonography has become more and more important in the diagnosis of rheumatic diseases. With the development of high-frequency realtime transducers, detailed images of the musculoskeletal system can be provided. Furthermore, sonography or echocardiography is able to detect systemic manifestations of connective tissue diseases. Compared to plain films, which mainly evaluate bony lesions of inflammatory joint diseases, sonography is used to assess non-bony abnormalities (synovial membrane, cartilage, menisci, tendons) and synovial space. Pannus and effusion as indicators of inflammatory rheumatic disease can easily be examined by sonography. However, sonographic findings in rheumatic diseases are mostly nonspecific and can rarely be used to distinguish between different diagnoses, which is sometimes possible using plain x-rays (i.e., pencil-in-cup). Sonography has proven to be a meaningful diagnostic tool in evaluating tumors in subcutaneous tissue or muscles. The diagnostic results of musculoskeletal sonography are today compared to those obtained by computed tomography (CT) and magnetic resonance imaging (MRI). Although musculoskeletal MRI can visualize bony and non-bony structures at the same time, sonography is still of particular interest in the diagnosis of rheumatic diseases, because it is a noninvasive, widely available, relatively inexpensive imaging modality which can be rapidly performed and repeated.

Bone scintigraphy is a modern method of low specificity but very high sensitivity in determining early changes in bone metabolism. There is a relationship between excessive skeletal metabolic disorders of the bone and the appearance of foci of maximum radionuclide uptake, or "hot spots". This distribution of radionuclide uptake has a specific character. In a retrospective study, we investigated the distribution of hot spots in 92 patients with various forms of psoriatic disease. Hot spots were found at and near to joints only. In enthesopathies hot spots are not found, because of lack of substance. They do, however, show signs suggesting a major disorder in collagen metabolism. Hot spots indicate a rather acute degree of skeletal involvement in psoriatic disease and are also frequently found in very active phases of psoriatic disease. Therapy-induced regression is possible. Spontaneous regression was observed only in the case of hot spots of short duration. The correlation of scintigraphic findings with X-rays shows that hot spots are signs of maximal focal metabolic activity. In a high percentage of cases they are leading up to a state of destruction, which can be shown on X-rays later. Among other parameters, they indicate the likelihood of skeletal involvement in psoriatic disease. Moreover, they indicate a high risk of "psoriatic arthritis".

Soft tissue calcification at the margin of the tuberosity of the distal phalanges of the fingers occurs in 7% of normal adults, varying between 0 and 14.5%, depending on age and sex. This type of calcification is least common in the little finger. The fingers on the right are more frequently affected than those on the left. Presumably this calcification results from mechanical injury ot the collagen fibres close to their insertion into the margin of the tuberosity.