Autoimmune Diseases with a Rash

1. Systemic Lupus Erythematosus (SLE)

• The hallmark is the malar (butterfly) rash: confluent, macular or papular erythema appearing symmetrically on the cheeks and bridge of the nose, lasting days to weeks.
• A key distinguishing feature: spares the nasolabial folds (a sun-protected area). This separates it from rosacea and dermatomyositis, both of which involve the nasolabial folds.
• Triggered and worsened by UV light. Over 90% of SLE patients show an abnormal skin reaction to UV provocation testing.
• Can generalize to any photosensitive area of the body. On the hands, erythema typically spares the MCP joints and sits between the interphalangeal joints - the opposite of dermatomyositis.
• Heals without scarring (unlike discoid lupus).

• Chronic, scarring plaques - active lesions shown here on the lateral face and ear:

• Palpable purpura (lower extremities) - cutaneous leukocytoclastic vasculitis
• Livedo reticularis / livedo racemosa - violaceous, net-like pattern; strongly associated with antiphospholipid syndrome (APS)
• Bullous lupus - rare subepidermal blistering from anti-type VII collagen antibodies
• Periungual erythema - dilated capillaries at the nail base (also seen in scleroderma and MCTD)
• Lupus tumidus - edematous, erythematous smooth plaques; highly photosensitive; favors the zygomatic region

2. Dermatomyositis

• Pink-violet discoloration of the eyelids and periorbital skin, often with edema. Can be subtle. Shown here:

• Flat-topped, erythematous-to-violaceous papules on the knuckles (MCPs and interphalangeal joints) - the exact opposite distribution from SLE on the hands.
• Gottron sign = involvement of the elbows and/or knees.

• V-neck sign (upper chest), shawl sign (upper back), holster sign (lateral thighs).
• Pink-violet hue; can be misdiagnosed as psoriasis when on extensor surfaces.

• Nail-fold telangiectasias with capillary dropout ("ragged cuticles")
• Intensely pruritic - pruritus is uncommon in lupus and helps distinguish the two
• Calcinosis cutis - especially in juvenile dermatomyositis (25-70% of pediatric cases)

3. Psoriatic Arthritis / Psoriasis

• Classic appearance: sharply demarcated, thick, erythematous plaques covered by dry silvery-white scales, predominantly on extensor surfaces (elbows, knees).
• Inverse psoriasis lacks silvery scaling and instead presents as erythematous plaques in skin folds (inguinal, inframammary, axillary).
• Nail pitting and onycholysis are common associated features.

4. Systemic Sclerosis (Scleroderma)

• Skin tightening beginning with swollen, puffy digits, then progressive tightening of the hands, face, and (in diffuse SSc) trunk and legs
• Telangiectasias on the face, hands
• Digital ulcers at fingertips
• Periungual erythema with capillary dropout (more prominent than in SLE)
• Raynaud phenomenon often precedes cutaneous involvement by years

5. Adult-Onset Still Disease (AOSD)

• Evanescent, salmon-colored blanching rash that appears during daily spiking fevers (peaking late in the day)
• Lasts only 1-2 hours, coinciding with fever spikes
• Associated with high ferritin, arthritis, and lymphadenopathy

6. ANCA-Associated Vasculitis

• Palpable purpura - non-blanching, purpuric rash from necrotizing small-vessel vasculitis
• Present for days, often palpable; biopsy is essential for diagnosis
• Associated with conditions like granulomatosis with polyangiitis (GPA) and microscopic polyangiitis

Quick Diagnostic Summary

Autoimmune Diseases with a Whole-Body (Generalized) Rash

1. Generalized ACLE (Acute Cutaneous Lupus Erythematosus) - SLE

• Widespread macular or maculopapular erythema in a photosensitive distribution across any area of the body - arms, trunk, legs, hands
• Palmar surfaces, dorsa of hands, and extensor surfaces of fingers commonly involved
• On the hands, erythema sits between the MCP and IP joints (sparing the joint surfaces themselves - opposite of dermatomyositis)
• Severe cases can progress to a TEN-like bullous eruption when interface inflammation at the dermo-epidermal junction causes epidermal detachment
• Heals without scarring; may leave post-inflammatory hyperpigmentation

2. Subacute Cutaneous Lupus Erythematosus (SCLE)

• Two forms: (1) papulosquamous (resembling psoriasis) or (2) annular-polycyclic with peripheral scale and central clearing - both forms can coexist in the same patient
• Strongly associated with anti-SSA/Ro antibody and HLA-DR3
• Drug-induced SCLE is common: ACE inhibitors, hydrochlorothiazide, terbinafine, calcium channel blockers are key culprits. Onset can be delayed up to 6 years after starting the drug.
• Lesions last weeks to months and heal without scarring

3. Dermatomyositis - Photodistributed Poikiloderma

• Photodistributed poikiloderma: involves the upper chest (V-neck sign), upper back (shawl sign), and lateral thighs (holster sign)
• Can cover most of the body surface in a photosensitive distribution
• Pink-violet coloration with telangiectasias, atrophy, and mottled pigmentation
• Often intensely pruritic (which helps distinguish it from SLE)
• Can mimic psoriasis when plaques occur on extensor surfaces, or mimic cutaneous T-cell lymphoma when poikiloderma is widespread

4. Pemphigus Vulgaris

• Anti-desmoglein antibodies (IgG) attack epidermal cell adhesion, producing flaccid, thin-walled blisters that rupture almost immediately into painful erosions
• Erosions can become extensive over the entire body surface - oozing, bleeding, crusting with no tendency to heal spontaneously
• Nikolsky sign: gentle lateral pressure on skin slides off the upper epidermis (sign of active disease)
• Mucous membranes always involved (oral erosions in essentially 100% of cases); can also affect throat, esophagus, genitalia, conjunctivae
• Without treatment, erosions become generalized and life-threatening

5. Erythrodermic / Generalized Pustular Psoriasis

• >90% of body surface covered in red, scaling skin
• Typical psoriatic features are often lost; skin becomes uniformly red and exfoliating
• Can be precipitated by abrupt withdrawal of systemic steroids, or by UVB phototherapy

• Waves of sterile subcorneal pustules on an erythematous base, spreading over the entire body
• Systemic features: fever, malaise, leukocytosis
• Can be life-threatening due to fluid/electrolyte loss

6. Diffuse Cutaneous Systemic Sclerosis (dcSSc)

• Begins with sclerodactyly (finger tightening), then ascends from distal to proximal limbs, and eventually spreads to the trunk - distinguishing it from limited SSc which stays below the elbows/knees
• Associated with anti-Scl-70 (topoisomerase I) antibodies
• Raynaud phenomenon, telangiectasias, and digital ulcers accompany the skin changes

Quick Summary Table