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DR15.1-3 | Pyoderma — PBL Case

CLINICAL SETTING

You are a MBBS intern posted in the Dermatology OPD at a district hospital in Tamil Nadu. It is a busy Monday morning and three members of the same family — a grandmother, her adult son, and his 5-year-old daughter — arrive together, each with a different skin problem that developed over the past week. The family shares a two-room home and the son works as a fisherman, spending long hours in humid conditions.

Trigger 1: Three Patients, Three Problems

Examination findings: **Patient A — Grandmother, 68 years, known diabetic (HbA1c 9.4%):** A 6 cm area of bright red, tense, palpably raised skin on the left cheek, with a sharply demarcated edge. Temperature 38.6°C. She says it began two days ago as a red patch that 'grew overnight.' She feels cold and shivery. **Patient B — Son, 38 years:** Multiple interconnected painful swellings on the back of the neck, 8 cm in total, with pus discharging from four separate openings. He is afebrile but the area is very tender. He mentions he has had similar 'boils' twice before in the last year, always on the neck or axillae. **Patient C — Granddaughter, 5 years:** Multiple honey-coloured crusted lesions around the mouth and on the chin, with a few small intact vesicles. No fever. She has been scratching her face.

DISCUSSION POINTS

  • Name the most likely diagnosis for each of the three family members. What morphological features and depth of skin involvement led you to each diagnosis?
  • Which single patient requires the most urgent assessment and why? What systemic risk factor makes one of these cases more complex?
  • The family shares bedding and towels. Which of these conditions poses the greatest risk of household spread, and through what mechanism?
Click to reveal Trigger 2: Investigation and Organism Identification (discuss previous trigger first!)

Trigger 2: Investigation and Organism Identification

You send appropriate swabs from all three patients. - **Patient A (grandmother):** Blood cultures are sent. WBC 14,200/µL with neutrophilia. The skin edge is intensely painful and hot but the Nikolsky sign is negative. - **Patient B (son):** Wound swab Gram stain shows Gram-positive cocci in clusters. You note that his previous 'boil' was treated with amoxicillin with incomplete response. - **Patient C (granddaughter):** Gram stain from a vesicle base shows Gram-positive cocci in both clusters and chains. While reviewing Patient B further, you press firmly on the swelling edge and feel a subtle 'crackling' sensation in the upper thigh area, which was not the original complaint site. His leg pain is significantly greater than the visible skin findings suggest. Temperature is now 38.2°C.

DISCUSSION POINTS

  • For each patient, identify the most likely causative organism(s) and explain the pathogenic mechanism responsible for the clinical appearance — specifically, why does Patient A's lesion have a raised, demarcated margin?
  • The 'crackling sensation' and disproportionate pain in Patient B's thigh is a new finding. What does this suggest, and how does it change your immediate management plan?
  • Patient B's previous incomplete response to amoxicillin raises a concern. What organism should you consider, and what directed therapy would you select while awaiting full sensitivities?
Click to reveal Trigger 3: Treatment Decisions and Drug Adverse Effects (discuss previous trigger first!)

Trigger 3: Treatment Decisions and Drug Adverse Effects

Culture results return the next morning: - **Patient A:** Blood cultures negative. Wound swab: Group A Streptococcus (Streptococcus pyogenes), fully penicillin-sensitive. - **Patient B's thigh:** CT scan confirms gas in the fascial plane of the medial thigh. Wound culture grows MRSA. - **Patient C:** Mixed growth Staphylococcus aureus + Streptococcus pyogenes, MSSA. The surgical team has been called for Patient B. While you wait, you must initiate antimicrobials for all three. Patient A's daughter asks you: 'Doctor, my mother is allergic to penicillin — she got a rash with amoxicillin 10 years ago. What will you give her instead?' For Patient C, your colleague suggests prescribing a 5-day course of oral co-trimoxazole. You are uncertain this is appropriate.

DISCUSSION POINTS

  • What is the appropriate antibiotic for Patient A (Strep pyogenes erysipelas, penicillin allergy history)? Explain your choice and its relevant adverse effect profile.
  • What is the emergency management for Patient B? Why must antibiotics alone not be the treatment for confirmed NSTI? Name one broad-spectrum regimen appropriate for polymicrobial NSTI coverage.
  • Critically evaluate the suggestion to use oral co-trimoxazole for Patient C's localised facial impetigo. What would you prescribe instead, and why does this align with antimicrobial stewardship principles? Discuss one specific adverse effect of co-trimoxazole that reinforces the stewardship argument.
Click to reveal Trigger 4: Outcomes, Complications, and Prevention (discuss previous trigger first!)

Trigger 4: Outcomes, Complications, and Prevention

One week later: - Patient A responds well to antibiotics; her erysipelas resolves, but she develops a new episode 3 months later on the same leg. - Patient B survives after emergency fasciotomy and debridement of the medial thigh; his MRSA required IV linezolid in the ICU. He is now being discharged. - Patient C's impetigo cleared within 5 days. However, two weeks later she develops periorbital oedema and her urine is brown-coloured. Her BP is 130/90 mmHg. Urine dipstick: 3+ protein, 3+ blood. The family asks you: 'Is there anything we could have done to prevent all this from happening?'

DISCUSSION POINTS

  • Patient C has developed a complication. What is the diagnosis? Which organism is responsible, and why is this complication not prevented by antibiotic treatment of the skin infection?
  • Patient A's recurrent erysipelas suggests a predisposing factor. What local and systemic factors predispose to recurrent erysipelas, and what preventive strategy can reduce recurrence?
  • Patient B is being discharged after MRSA NSTI. What decolonisation strategy would you recommend, and what household hygiene counselling would you provide to the family to reduce the risk of MRSA transmission?
  • Reflecting on all three cases: what single clinical sign in Patient B, if recognised earlier on the day of admission, should have immediately triggered urgent surgical referral before the CT scan?