Rheumatic immune diseases, also known as “rheumatism” or “rheumatism”, are now known as “rheumatism” in the medical community because recent medical research has found that these diseases are caused by abnormalities in the body’s immune system. immune diseases”. These diseases are systemic in nature and can involve many organs and systems throughout the body, with the skin being one of the most commonly affected organs. The rashes of rheumatic immune diseases are complex, as the same disease and the same patient can present with different rashes, and the same rash can appear in different rheumatic immune diseases. Therefore, it is important to correctly identify rashes associated with rheumatologic diseases and to consult a rheumatologist early for early diagnosis of rheumatologic diseases. To help you understand what kind of rash to suspect to rheumatic immune disease, some common rashes are introduced. Butterfly-shaped erythema: This kind of erythema often appears on the cheeks and manifests as bright red or purplish red edematous erythema slightly above the skin surface, which may be accompanied by desquamation and blistering, etc. It is mainly seen in lupus erythematosus. Blood immune system changes are also usually present, such as the presence of antinuclear antibodies and positive double-stranded DNA manifestations. The rash of discoid lupus erythematosus: the limited rash involves only the head and face. Disseminated discoid lupus also involves the hands, feet, extremities, and trunk, and may rarely develop into systemic lupus erythematosus. The rash starts as a small papule and gradually expands into dark red patches with adherent scales. The rash is most commonly seen on the cheeks of the face and the back of the nose, followed by the auricles, the outer neck, the scalp, the mouth and lips, and the back of the hands and chest, often with bilateral but asymmetric involvement. Changes in the blood immune system, such as the presence of antinuclear antibodies, and additionally a decrease in the white blood cell count may be present. Figure 2: Subacute cutaneous lupus erythematosus rash: The rash is mostly distributed on the face, ears, upper chest, back, shoulders and back of the hands, and mainly presents as papulosquamous and annular erythematous type. Routine blood tests show decreased total white blood cell count, increased blood sedimentation and positive rheumatoid factor. Erythema nodosum rash: It is an inflammatory disease that occurs in the subcutaneous fat. The rash is prevalent in the anterior tibia, often as symmetrical painful nodules, red elevations on the skin surface, 1 cm in diameter in size, with pressure pain, without rupture, able to fade on their own, and can recur. The pathological tissue is markedly edematous in the middle and lower dermis and subcutaneously, with peritubular infiltration around sweat glands and blood vessels (Figure 4). Figure 4: Erythema nodosum Raynaud’s phenomenon: spasm of small finger (toe) arteries occurs suddenly under the stimulation of cold or emotional stress. Typical symptoms are white and purple coloring of the fingers or toes after exposure to cold or emotional stress, which may be accompanied by local numbness or tingling. Raynaud’s phenomenon is often associated with connective tissue diseases and can be seen in more than 90% of scleroderma and mixed connective tissue diseases, more than 20% of lupus erythematosus, etc. In rheumatologic diseases, the rash is mainly found in patients with psoriatic arthritis, with lesions on the scalp and the extremities, especially the elbows and knees, in a scattered or generalized distribution. This feature has diagnostic significance for psoriasis. It is accompanied by superficial lymph node enlargement and elevated white blood cell count. The skin has a reticulated cyanotic pattern, which is aggravated by cold and disappears after warmth. The rash is located on the joint extensions, mostly at the elbow, metacarpophalangeal and proximal interphalangeal joints, but also at the knee and inner ankle skin, and appears as erythema with scales, which can be accompanied by skin atrophy and hypopigmentation, and is valuable for the diagnosis of dermatomyositis. It is also associated with elevated serum myoglobin, normal or reduced white blood cell count, and 2/3 may have increased blood sedimentation. Blood IgG, IgA, IgM, immune complexes, and a2 and Y globulins may be increased. As shown in Figure 8 Figure 8 Gottron’s rash Towards positive rash: periorbital edematous dark purple-red rash, seen in 60% to 80% of patients, characteristic rash for dermatomyositis. Muscle pathology suggests type I and type II myofiber necrosis, elevated skeletal muscle myokines, and glutamic aminotransferase, glutamic aminotransferase, and lactate dehydrogenase are also commonly elevated. Figure 9. Fig. 9 Pityriasis militans In rheumatic immune diseases purpura, urticaria-like rash, alopecia areata, cutaneous vasculitis, ulcers, skin hyperpigmentation or hypopigmentation, photosensitive rash, purulent skin keratosis, annular erythema, etc. can also be present, but lack specificity.