Autoimmune blistering, connective-tissue and vascular patterns
Autoimmune blistering disease
Pemphigus vulgaris: flaccid blisters, mucosal involvement, positive Nikolsky sign, intercellular IgG on immunofluorescence, anti-desmoglein 3. Bullous pemphigoid: tense blisters in older patients, anti-BP180/BP230, linear IgG and C3 at the basement membrane, tissue eosinophils. Dermatitis herpetiformis: intensely itchy grouped vesicles on elbows and knees, granular IgA in dermal papillae, gluten-sensitive enteropathy.
Connective tissue disease
Lupus: acute malar rash, subacute annular photosensitive lesions with anti-Ro, discoid scarring lesions. Check ANA, anti-dsDNA and complement. Dermatomyositis: heliotrope rash, Gottron papules, shawl sign, mechanic's hands; disease features and myositis antibodies can inform an individualized malignancy-risk assessment, and screening should follow the relevant clinical risk framework. Systemic sclerosis: sclerodactyly, Raynaud phenomenon, telangiectasia, calcinosis and abnormal nailfold capillaroscopy.
Cutaneous clues to systemic disease
Acanthosis nigricans (insulin resistance, malignancy), pyoderma gangrenosum (IBD and hematological disease), erythema nodosum (streptococcus, sarcoidosis, IBD, drugs), Sweet syndrome, necrobiosis lipoidica (diabetes), and palpable purpura (check urinalysis, renal function, blood pressure).
Traps
- Calling every photosensitive rash "lupus".
- Forgetting malignancy screening in new adult dermatomyositis.
- Treating a low-titre ANA as diagnostic.
- Missing renal involvement in IgA vasculitis , always check urine.
Clinical integration
Skin change plus systemic features (fever, weight loss, myalgia, arthralgia): investigate for connective tissue disease or paraneoplastic process rather than reaching for topical steroid.
Specimen and mechanism
Blistering assessment must connect the cleavage plane with the immune target and the phenotype. Loss of keratinocyte cohesion differs from separation at the basement-membrane region. Direct immunofluorescence depends on specimen selection and handling, while indirect testing and antigen-specific assays provide complementary information. The same broad linear basement-membrane pattern can require further distinction among diseases; a salt-split result is also interpreted with the target and clinical presentation rather than as an isolated label.
Connective-tissue disease can produce interface change, photosensitivity, vascular abnormalities or specific adnexal findings. An ANA result alone does not diagnose systemic lupus, and a skin association does not prove an unmeasured internal complication. Ask about muscle function, respiratory symptoms, renal findings, mucosal disease and vascular manifestations when clinically relevant. Palpable purpura can indicate cutaneous small-vessel disease with or without systemic involvement. Biopsy timing, urine assessment, renal function and other investigations depend on the actual case. Immunosuppressive treatment introduces infection, organ-toxicity and reproductive considerations. A recognizable antibody or immunofluorescence pattern improves diagnostic reasoning but is not a complete regimen or a guarantee of future outcome.