What are the laboratory findings for a patient presenting with pruritic (itchy) rash?

From the Guidelines

When evaluating an itchy rash, a comprehensive approach is necessary to determine the underlying cause, and I recommend starting with a thorough history and physical examination, followed by laboratory tests such as a complete blood count (CBC) with differential, comprehensive metabolic panel (CMP), and thyroid function tests, as suggested by the guidelines for the management of atopic dermatitis 1. The diagnosis of atopic dermatitis is made clinically and is based on historical features, morphology and distribution of skin lesions, and associated clinical signs, and formal sets of criteria have been developed to aid classification, such as the Hanifin and Rajka criteria and the UK Working Party diagnostic scheme 1. In addition to laboratory tests, a skin biopsy may be necessary to diagnose certain dermatological conditions, and it is essential to rule out other etiologies of the skin problem, such as infection, an effect of another drug, or a skin condition linked to another systemic disease 1. The management of generalized pruritus in adults without an underlying dermatosis involves a step-wise approach, starting with the treatment of underlying conditions, such as iron deficiency or overload, and the use of topical and systemic therapies, such as emollients, corticosteroids, and antihistamines, as recommended by the British Association of Dermatologists' guidelines 1. Some key points to consider when evaluating an itchy rash include:

• A thorough history and physical examination to determine the underlying cause
• Laboratory tests, such as CBC, CMP, and thyroid function tests, to rule out underlying conditions
• Skin biopsy to diagnose certain dermatological conditions
• Treatment of underlying conditions, such as iron deficiency or overload
• Use of topical and systemic therapies, such as emollients, corticosteroids, and antihistamines, to manage generalized pruritus. It is also important to consider the potential for immune-related adverse events in patients treated with immune checkpoint inhibitor therapy, and to follow the guidelines for the management of these events, as recommended by the American Society of Clinical Oncology 1.

From the Research

Itchy Rash Labs

• Itchy rash can be caused by various factors, including xerosis and eczema, as stated in the study 2.
• The diagnosis and treatment of pruritus, which is the medical term for itchy rash, can be challenging due to the lack of a good body of evidence from high-quality trials, as mentioned in the study 2.
• Nonpharmacologic therapy, including frequent moisturization, can improve symptoms in most patients with itchy rash, as suggested in the study 2.
• If nonpharmacologic therapy fails, further investigations are warranted to guide subsequent treatment with cause-specific topical and systemic approaches, as stated in the study 2.

Causes of Itchy Rash

• Itchy rash can be caused by primary pruritic dermatoses or can manifest in the absence of a primary pruritic skin rash, as mentioned in the study 3.
• Cutaneous pruritus, which refers to itchy rash without a primary pruritic skin rash, can be classified into localized and generalized cutaneous pruritus, as stated in the study 3.
• Systemic diseases, such as disorders of iron metabolism, chronic kidney disease, and chronic liver disease, can cause generalized cutaneous pruritus, as mentioned in the study 3.

Treatment of Itchy Rash

• Various treatment approaches are available for cutaneous pruritus, including device-based physical therapies and medications that act on the itch-perception processing pathway, as stated in the study 3.
• Topical anti-inflammatory treatments, such as glucocorticoids and calcineurin inhibitors, can be used to manage atopic dermatitis, a common cause of itchy rash, as suggested in the study 4.
• Alternative glucocorticoids, such as betamethasone and deflazacort, can be used in patients with adverse reactions to systemic glucocorticoids, as mentioned in the study 5.
• Allergic-type reactions to corticosteroids can occur, and clinicians should be aware of this possibility when treating patients with itchy rash, as stated in the study 6.