Dermatology · Papulosquamous Disorders
The facts most likely to be tested
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Psoriasis is a T-cell mediated chronic inflammatory disease characterized by hyperproliferation of keratinocytes in the epidermis.
The classic physical exam finding is a well-demarcated, erythematous plaque with silvery micaceous scale typically found on extensor surfaces.
Removal of the scale results in punctate bleeding, a phenomenon known as the Auspitz sign.
Mechanical trauma to the skin, such as a scratch or sunburn, induces new psoriatic lesions at the site of injury, known as the Koebner phenomenon.
Psoriatic arthritis presents as an asymmetric oligoarthritis often involving the distal interphalangeal (DIP) joints and associated with dactylitis.
Nail involvement in psoriasis frequently manifests as pitting, onycholysis, and the oil drop sign.
First-line treatment for localized plaque psoriasis is high-potency topical corticosteroids combined with vitamin D analogs like calcipotriene.
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A 34-year-old male presents with a chronic skin rash on his elbows and knees that has persisted for several months. Physical examination reveals well-demarcated, erythematous plaques covered with silvery micaceous scales. When the patient scrapes the surface of the lesion, he develops punctate bleeding. He also reports morning stiffness in his fingers and notes that his distal interphalangeal joints appear swollen and tender.
What is the most likely diagnosis and the most appropriate initial systemic management if topical therapy fails?
Psoriasis and Psoriatic Arthritis; Methotrexate
The patient exhibits the classic Auspitz sign and extensor surface distribution of psoriasis, while the DIP joint involvement and dactylitis indicate psoriatic arthritis, which requires systemic therapy like methotrexate when severe.
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High yield triage
Etiology / Epidemiology
Chronic immune-mediated disease with bimodal age distribution (20s and 50s) and strong genetic predisposition (HLA-Cw6).
Clinical Manifestations
Well-demarcated salmon-colored plaques with silvery micaceous scales; classic Auspitz sign and Koebner phenomenon.
Diagnosis
Clinical diagnosis; skin biopsy is the gold standard if presentation is atypical.
Treatment
High-potency topical corticosteroids are first-line; avoid systemic steroids due to risk of pustular flare.
Prognosis
Chronic condition; 30% of patients develop psoriatic arthritis requiring early rheumatology referral.
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Epidemiology & Etiology
Psoriasis affects 2-3% of the population, often triggered by streptococcal pharyngitis (guttate type) or physical trauma. It is a T-cell mediated autoimmune disease with a strong HLA-Cw6 association. Environmental triggers include stress, alcohol, and medications like lithium or beta-blockers.
Pertinent Anatomy
Predominantly affects extensor surfaces (elbows, knees) and the scalp. The disease involves the epidermis and dermis, characterized by rapid keratinocyte turnover.
Pathophysiology
Dysregulated T-cell activation (Th1/Th17) leads to cytokine release (IL-12, IL-23, TNF-alpha). This causes hyperproliferation of keratinocytes and shortened cell cycle time from 28 days to 3-5 days. The resulting accumulation of immature cells creates the characteristic parakeratosis.
Clinical Manifestations
Patients present with well-demarcated plaques covered in silvery micaceous scales. The Auspitz sign (pinpoint bleeding upon scale removal) and Koebner phenomenon (lesions at sites of trauma) are pathognomonic. Pustular psoriasis is a medical emergency that can lead to sepsis and electrolyte imbalance.
Diagnosis
Diagnosis is primarily clinical. If uncertain, a punch biopsy reveals Munro microabscesses and Acanthosis. No specific laboratory values are diagnostic, but HLA-B27 may be positive in patients with associated spondyloarthropathy.
Treatment
First-line therapy for localized disease is high-potency topical corticosteroids (e.g., clobetasol). For extensive disease, phototherapy (UVB) is indicated. Systemic corticosteroids are strictly contraindicated as they trigger rebound flares. Biologics like adalimumab are reserved for refractory cases or severe psoriatic arthritis.
Prognosis
Psoriasis is a lifelong condition with a high burden of metabolic syndrome and cardiovascular disease. Patients must be screened for psoriatic arthritis using the PEST questionnaire. Early intervention is critical to prevent permanent joint deformity.
Differential Diagnosis
Seborrheic dermatitis: greasy yellow scales on the face/scalp
Tinea corporis: central clearing with active, scaly borders
Lichen planus: purple, polygonal, pruritic papules
Pityriasis rosea: herald patch followed by Christmas tree distribution
Secondary syphilis: generalized rash involving palms and soles
Go deeper
Psoriasis is an idiopathic, genetic autoimmune skin disease managed by dermatologists using topical steroids, systemic immunosuppressants, and targeted biologic therapies. Diet is considered largely irrelevant beyond general weight management.
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