Laboratory and imaging investigations for associated systemic disease

Overview

Dermatological investigation beyond skin biopsy spans targeted blood tests (autoantibodies, inflammatory markers, specific serology) and imaging (for staging skin malignancy or assessing deeper soft tissue extent) - selected based on the specific clinical question rather than as a routine panel for every skin presentation
Most skin conditions are diagnosed clinically or with biopsy alone; additional laboratory/imaging investigation is reserved for specific scenarios (suspected systemic association, staging confirmed malignancy, monitoring systemic treatment)

Autoantibody testing (ANA, specific bullous disease serology, myositis-specific antibodies) supports diagnosis when a skin finding suggests an underlying systemic autoimmune/connective tissue disease
Imaging (ultrasound for nodal staging in melanoma, CT/PET for staging locally advanced or metastatic skin cancer) is used once malignancy is confirmed and staging is required, not as a screening tool for undiagnosed skin lesions

Targeted testing based on the specific differential being considered - e.g. ANA/ENA panel when a photosensitive rash suggests lupus, myositis-specific antibodies when Gottron's papules/heliotrope rash suggest dermatomyositis
Baseline and monitoring bloods (FBC, LFTs, renal function) are required before and during many systemic dermatological treatments (methotrexate, biologics, isotretinoin) given their specific toxicity profiles

Results directly inform whether a skin finding represents an isolated dermatological condition or a cutaneous manifestation of systemic disease requiring broader multidisciplinary management
Pre-treatment and monitoring bloods for systemic therapy are a standard, non-negotiable part of safe prescribing for these agents

Connective tissue disease serology (see laboratory investigations), melanoma sentinel node/staging imaging, systemic treatment monitoring bloods (methotrexate, biologics, isotretinoin)

Investigation should be targeted to a specific clinical question suggested by the history/examination, rather than ordered as an undirected panel - most dermatological diagnoses remain clinical or biopsy-based, with laboratory/imaging testing reserved for specific systemic-association or staging/monitoring purposes

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