Skin Rash OSCE - Cellulitis

Case Overview

• Age/Sex: 65-year-old female
• Occupation: Retired schoolteacher
• Setting: Emergency Department, brought by daughter
• Chief complaint: "Rash on my left lower leg — it's very painful and hot"

Patient Script

Who I Am

I'm 65, I used to teach primary school, and I live with my daughter since my husband died last year.

What Brings Me In

My left leg has been getting red, swollen and very painful for a few days and I have a fever — I felt faint this morning so my daughter brought me in.

My Story

It started about 3 days ago as a small area of redness behind my left ankle after I was gardening. I thought it was just a scratch from a thorn, but over the next 48 hours it spread up my lower leg and got much more painful. I developed shivers and a fever yesterday and today I felt very weak and nearly fainted when I stood up. The skin is now very red and warm and there are a couple of small blisters that appeared today. I also noticed a red streak going up toward my knee. I have diabetes and sometimes my legs swell; this feels different and much worse.

My Medical Background

• Type 2 diabetes for 18 years (usually on tablets and sometimes insulin)
• Hypertension
• Chronic kidney disease stage 3
• Previous deep vein thrombosis in the left leg 5 years ago (treated with anticoagulation then)
• Medications: metformin 500 mg twice daily, basal insulin at night (variable doses), ramipril 5 mg daily, simvastatin 20 mg nightly, aspirin 75 mg daily, over-the-counter turmeric supplement occasionally
• Allergies: penicillin — rash as a teenager (itchy red rash; not sure if swelling)
• Social: lives with daughter, non-smoker, drinks 1–2 units alcohol/week
• Family: mother had diabetes, father had heart disease

What I Think & Worry About

• I think it might be an infection from a thorn or bite when I was gardening.
• I’m worried it could spread and I might lose my leg or be admitted to hospital.
• I expect you might give me something to stop the infection and some pain relief; I don’t want to go back to being very weak or faint.

If You Ask Me About Other Symptoms...

• Pain: The pain in the leg is sharp and constant, 8/10, worse when I move or stand.
• Fever/shivers: I had shivers and a high fever yesterday and have felt hot and sweaty today.
• Discharge: There was no pus until this morning when a tiny bit of fluid came out of a blister.
• Breathlessness/chest pain: No chest pain; slightly short of breath when walking up stairs but that's usual for me.
• Urine: I passed urine less often today but it looks darker than normal.
• Recent treatments: I had a urinary tract infection treated with a 3-day course of trimethoprim about 6 weeks ago.
• Skin history: I get itchy eczema occasionally and wear elastic stockings for leg swelling; I also use a moisturizing cream on my legs.
• Mobility: Usually mobile at home with a stick; today I needed help standing.
• Red herrings I might mention if asked: I used a new soap last week, was gardening and got some tiny scratches, and I took a herbal cream two days ago from a market stall thinking it might help.

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Clinical Summary

Examination

• General: alert but febrile and unwell; diaphoretic; mildly confused when standing
• Vitals: Temperature 39.0°C; Heart rate 112 bpm; Blood pressure 95/60 mmHg; Respiratory rate 22/min; SpO2 96% on room air
• Cardiorespiratory: Heart sounds normal, lungs clear
• Left lower leg inspection: extensive erythema from ankle to mid-calf measuring approximately 20 x 15 cm, ill-defined margins, warmth to touch, tender throughout, two small tense blisters anteriorly, mild central pitting oedema
• Palpation: no crepitus; lymphangitic streaking proximally toward knee; pain on passive stretch of ankle is present but not extreme
• Vascular: dorsalis pedis and posterior tibial pulses palpable but slightly diminished; capillary refill 3 seconds
• Neurological (limb): reduced light-touch sensation over feet consistent with diabetic peripheral neuropathy
• Other: no obvious fluctuance to suggest a discrete abscess; no signs of necrosis

Investigations

• CBC: WCC 18.2 x10^9/L (neutrophils 15.6 x10^9/L) (leukocytosis with neutrophilia)
• CRP: 220 mg/L (markedly elevated)
• Lactate: 3.0 mmol/L (borderline elevated — concern for systemic compromise)
• U&E: Na 136 mmol/L, K 4.4 mmol/L, Creatinine 160 µmol/L (baseline ~130), eGFR ~40 mL/min/1.73m2
• Blood glucose: 16 mmol/L (hyperglycaemia)
• Blood cultures: taken (pending)
• Wound swab: obtained from blister fluid (pending)
• Doppler US left leg venous study: arranged to exclude DVT (result pending)
• Plain X-ray left leg: no subcutaneous gas identified

Diagnosis

• Primary: Acute severe cellulitis of the left lower leg with systemic inflammatory response (probable sepsis) — supported by rapidly spreading erythema, warmth, tenderness, blistering, lymphangitic streaking, fever, leukocytosis, elevated CRP and lactate, and relative hypotension.

• Differential diagnoses:

  • Deep vein thrombosis (DVT): relevant history of prior DVT and unilateral leg swelling, but the presence of fever, erythema, warmth, and elevated inflammatory markers favour infection; Doppler US to exclude DVT.
  • Necrotizing soft tissue infection: must be considered in severe presentations; less likely here because there is no crepitus, pain out of proportion is not clearly described, and X-ray shows no gas — surgical review advised if deterioration.
  • Infected venous ulcer / chronic stasis dermatitis with secondary infection: chronic leg changes and stockings are present as background, but the acute systemic features point to cellulitis.
  • Gout or septic arthritis: pain is more diffuse and skin changes are prominent; gout usually affects joints with intense joint pain and swelling rather than extensive skin erythema.
  • Contact dermatitis / allergic reaction: history of new soap and creams could explain rash but would not usually cause high fever, leukocytosis and spreading warmth.

Management

• Admit under medical team for inpatient care and monitoring.
• Immediate supportive care: intravenous fluids (careful given CKD and BP), paracetamol for fever, analgesia, oxygen if required, monitor vitals and urine output closely.
• Microbiological sampling: two sets of blood cultures prior to antibiotics; wound swab for culture and sensitivities.
• Empirical intravenous antibiotics promptly after cultures: start broad-spectrum cover for severe cellulitis with systemic compromise (e.g., IV vancomycin plus IV piperacillin–tazobactam) tailored to local guidelines and adjusted for renal function and penicillin allergy history — note patient reports penicillin allergy as a rash in youth; seek allergy clarification and consider allergy testing or alternative if necessary.
• Review need for MRSA coverage based on local risk factors and microbiology.
• Avoid compression bandaging while infection is active and limb is inflamed; elevate limb to reduce swelling.
• Urgent surgical review if any signs of deep infection, rapidly progressive necrosis, fluctuance suggesting abscess, or clinical deterioration.
• Imaging: Doppler ultrasound to exclude DVT and to look for any collection requiring drainage; consider MRI if deep space infection suspected.
• Optimize diabetes: insulin sliding scale or modify insulin regimen to improve glycaemic control while monitoring renal function.
• Review and adjust medications: hold nephrotoxic agents as appropriate; review anticoagulation history if previously anticoagulated.
• Plan for daily review of response to therapy, step-down to oral antibiotics when clinically improved and inflammatory markers falling, and physiotherapy / return to mobility once stable.

Key Learning Points

• Cellulitis typically presents with acute onset of spreading erythema, warmth, tenderness and systemic features; in diabetics the risk of severe infection and complications is higher.
• In severe presentations suspect systemic involvement/sepsis — obtain blood cultures, start empirical IV antibiotics promptly, provide supportive care, and request surgical review early if deep or necrotizing infection is a concern.
• Always consider and exclude important mimics (DVT, necrotizing fasciitis, contact dermatitis) and account for comorbidities (diabetes, CKD) when choosing investigations and antibiotic regimens.