Skin Rash OSCE - Psoriasis

Case Overview

• Age/Sex: 46-year-old male
• Occupation: Office worker (sedentary job)
• Setting: Primary care clinic
• Chief complaint: "Rash on my skin"

Patient Script

Who I Am

I'm 46, I work at a desk all day in IT, and I smoke about a pack a day.

What Brings Me In

I've had a rash for months that's getting worse and it's starting to bother me — it's scaly and won't go away.

My Story

About 6 months ago I noticed a small red patch on my right elbow. It didn't hurt much, just a bit itchy. Over the next few months it slowly got bigger and a similar patch came up on my left knee. In the last 3 weeks the patches have become more scaly and flaky and I've also noticed flaky skin on my scalp. When I scratch the scale sometimes it peels off and the skin bleeds a little. I tried an over-the-counter hydrocortisone cream and a fancy new skin lotion with no help. I also started using a new laundry detergent about 2 months ago which made some of my clothes smell different, but the rash started before that. I had a tooth abscess and took a short course of antibiotics (amoxicillin) about 3 weeks ago — that didn't seem to change the rash.

The rash comes and goes a bit with stress — I noticed it flared after a busy deadline last month. I don't have fevers or weight loss, but I felt a bit feverish once last month for a day. My father used to have "a skin problem" when he was younger that looked similar.

My Medical Background

• Past medical history: none significant
• Medications: none regularly; took amoxicillin 3 weeks ago for a dental infection
• Allergies: none known
• Social: current smoker ~20 cigarettes/day; drinks alcohol socially (about 10 6 units/week); sedentary occupation
• Family: father had a long-standing scaly skin condition; no known autoimmune disease in family

What I Think & Worry About

• I think it might be some kind of allergy from the detergent or something I ate.
• I'm worried it could be something serious or "incurable" since it keeps coming back.
• I'd like something that actually gets rid of it, not just creams that don't help.

If You Ask Me About Other Symptoms...

• Itchy: Yes, mild to moderate itch, worse with sweating or heat.
• Pain: Not really painful, only when it cracks and bleeds.
• Joints: Occasionally my fingers feel stiff in the morning for about 10 minutes, but no swollen painful joints.
• Nails: I 1've noticed tiny pits/dips on the thumbnails for a while.
• Systemic symptoms: No significant fevers, night sweats, or weight loss.
• Recent travel/animals: None relevant.
• New drugs: Apart from the short course of amoxicillin, no new regular medicines.

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Clinical Summary

Examination

• General: alert, comfortable, afebrile; BMI 29 kg/m2
• Vitals: T 36.7°C, HR 78/min, BP 130/80 mmHg, RR 14/min, SpO2 98% on air
• Skin: multiple well-demarcated, erythematous plaques with thick silvery-white scale on the extensor surfaces of both elbows and both knees; largest plaque ~6 cm in diameter; several smaller plaques on the trunk
• Scalp: confluent scaly plaques with adherent scales at the hairline
• Nails: pitting on thumbnails bilaterally
• Positive Auspitz-like sign: pinpoint bleeding when scale is gently removed from a plaque
• Musculoskeletal: no obvious synovitis; mild stiffness of finger joints reported but no swelling or reduced range of motion
• Lymph nodes: no significant lymphadenopathy

Investigations

• FBC: Hb 14.5 g/dL, WCC 7.2 x10^9/L, Platelets 250 x10^9/L (within reference ranges)
• CRP: 4 mg/L (normal/slightly low)
• ESR: 8 mm/hr (normal)
• Fasting glucose: 6.1 mmol/L (borderline)
• Skin swab: no pathogenic bacteria cultured
• Skin biopsy (if performed): hyperkeratosis, parakeratosis, acanthosis with elongated rete ridges and neutrophils in the stratum corneum (consistent with psoriasis)

Diagnosis

• Primary diagnosis: Plaque psoriasis (chronic stable plaque-type) — supported by well-demarcated erythematous plaques with silvery scale on extensor surfaces and scalp, nail pitting, positive family history, chronic relapsing course, and characteristic biopsy findings.

• Differential diagnoses:

  • Eczematous dermatitis (atopic/contact): pruritic and may be widespread, but distribution (extensors), thick silvery scale, and nail changes favor psoriasis.
  • Tinea corporis: can cause scaling plaques but usually shows central clearing and KOH would be positive; less likely here.
  • Seborrheic dermatitis: may affect scalp but lesions are less well-demarcated and more greasy-yellow scale.
  • Drug eruption or secondary syphilis: temporal relationship to antibiotics is weak and systemic signs/serology would help exclude.

Management

• Explain diagnosis and natural history: chronic relapsing course and common triggers (stress, alcohol, smoking, infections).
• Initial therapy for localized plaque disease (<10% BSA):
  • High-potency topical corticosteroid (e.g., betamethasone valerate) for affected plaques, with guidance on duration/skin site precautions.
  • Consider combination topical calcipotriol (vitamin D analogue) with steroid for increased efficacy.
  • Emollients regularly to reduce scale and fissuring.
• Scalp: use medicated shampoo (coal tar or tar-based) or topical steroid scalp solution/lotion; advise on application technique.
• Assess for psoriatic arthritis: ask focused joint history and examine joints; if suspicion persists (persistent joint pain/stiffness/swelling) refer to rheumatology.
• Lifestyle and comorbidity management: advise smoking cessation, reduce alcohol intake, weight loss, and screen/manage cardiometabolic risk (fasting glucose, lipids, BP control).
• Safety-net and follow-up: review response in 4 6 weeks; refer to dermatology if widespread disease, extensive or refractory disease, significant nail/difficult scalp involvement, or suspicion of psoriatic arthritis; consider phototherapy or systemic agents for moderate-severe disease.
• Consider skin biopsy if diagnosis remains uncertain despite clinical assessment.

Key Learning Points

• Plaque psoriasis commonly presents with well-demarcated erythematous plaques with silvery scale on extensor surfaces and scalp; nail pitting and a family history support the diagnosis.
• Always assess for psoriatic arthritis and cardiometabolic comorbidities; smoking and alcohol can exacerbate disease and affect management.
• Initial management of localized plaque psoriasis is topical therapy (potent steroid, topical vitamin D analogues) plus emollients and lifestyle modification; refer if severe, widespread, or treatment-resistant.