# Clinical Cases: Skin Infections

## Case 1: Necrotizing Fasciitis

### Patient Presentation
**Demographics:** 54-year-old male with diabetes

**Chief Complaint:** Rapidly spreading leg pain, swelling, and fever

**History of Present Illness:**
The patient developed a small abrasion on his right lower leg 3 days ago. Yesterday he noticed increasing redness and swelling. Over the past 12 hours, the pain has become severe and out of proportion to the visible findings. He developed fever, chills, and the affected area now has dusky discoloration with hemorrhagic bullae.

**Past Medical History:**
- Type 2 diabetes mellitus (poorly controlled, HbA1c 9.8%)
- Peripheral vascular disease
- Obesity

**Physical Examination:**
- Temperature: 39.4C
- Blood pressure: 88/54 mmHg
- Heart rate: 128 bpm
- Right lower leg:
  - Dusky, mottled skin with central necrosis
  - Hemorrhagic bullae
  - Crepitus on palpation
  - Severe tenderness extending beyond visible margins
  - **Pain out of proportion to examination findings**
  - Skin anesthesia over necrotic areas
- No dorsalis pedis pulse palpable on right

### Workup and Results

**Laboratory Studies:**
- WBC: 24,500/mcL with 15% bands
- Hemoglobin: 11.2 g/dL
- Platelets: 85,000/mcL
- Creatinine: 2.4 mg/dL
- Glucose: 385 mg/dL
- Sodium: 128 mEq/L
- Lactate: 6.2 mmol/L
- CRP: 32 mg/dL

**LRINEC Score:** 9 (high risk for necrotizing fasciitis)

**CT Scan:**
- Gas tracking along fascial planes
- Soft tissue thickening with fat stranding

**Wound Culture (intraoperative):**
- Polymicrobial: E. coli, Bacteroides fragilis, Peptostreptococcus

### Clinical Image

![Necrotizing Fasciitis](case_01_image.jpg)

*Clinical photograph demonstrating necrotizing fasciitis with characteristic dusky discoloration, hemorrhagic bullae, and tissue necrosis. The presence of crepitus and pain out of proportion are critical diagnostic clues.*

### Diagnosis
**Necrotizing Fasciitis Type I (Polymicrobial)**

Classification:
- Type I: Polymicrobial (mixed aerobic and anaerobic) - as in this case
- Type II: Monomicrobial (usually Group A Streptococcus)

### Discussion
This case illustrates necrotizing soft tissue infection:

- **Pain Out of Proportion**: The lecture emphasizes that pain out of proportion to examination findings is the clinical hallmark that should raise immediate concern for necrotizing fasciitis.

- **Type I vs Type II**: The lecture distinguishes Type I necrotizing fasciitis (polymicrobial) from Type II (monomicrobial, usually Group A Streptococcus). This patient has Type I with mixed aerobic and anaerobic organisms.

- **Surgical Emergency**: The lecture states that urgent surgical debridement is the most critical intervention. Antibiotics alone are insufficient and delays in surgery dramatically increase mortality.

- **Clindamycin Rationale**: The lecture notes that clindamycin is added to the antibiotic regimen because it inhibits toxin production, not just for anaerobic coverage.

### Treatment Plan
1. **Immediate Surgical Debridement:**
   - Emergent wide debridement of all necrotic tissue
   - Return to OR every 24-48 hours for re-exploration
   - Consider amputation if limb not salvageable

2. **Broad-Spectrum Antibiotics:**
   - Vancomycin (MRSA coverage)
   - Piperacillin-tazobactam (broad gram-negative and anaerobic)
   - Clindamycin (toxin production inhibition)

3. **Resuscitation:**
   - Aggressive IV fluid resuscitation
   - Vasopressor support if needed
   - ICU admission

4. **Supportive Care:**
   - Tight glucose control
   - Wound VAC after debridement
   - Consider hyperbaric oxygen (adjunctive)

5. **Monitoring:**
   - Serial lactate levels
   - Renal function
   - Signs of septic shock/organ failure

### Teaching Points
1. Pain out of proportion to exam is the hallmark of necrotizing fasciitis
2. Type I = polymicrobial; Type II = monomicrobial (usually GAS)
3. Urgent surgical debridement is the most critical intervention
4. Clindamycin inhibits toxin production
5. Crepitus and gas on imaging indicate gas-forming organisms

---

## Case 2: Herpes Zoster (Shingles)

### Patient Presentation
**Demographics:** 72-year-old female

**Chief Complaint:** Painful rash on left chest and back for 3 days

**History of Present Illness:**
The patient developed burning pain on her left chest 5 days ago, which she initially attributed to muscle strain. Two days later, she noticed grouped blisters appearing in the same area. The rash has spread along her left side in a band-like pattern but does not cross the midline. The pain is severe, described as burning and stabbing.

**Past Medical History:**
- Hypertension
- Osteoarthritis
- Chickenpox as a child
- Never received zoster vaccine

**Physical Examination:**
- Temperature: 37.8C
- Left T4-T5 dermatome:
  - Grouped vesicles on an erythematous base
  - Some vesicles with central umbilication
  - Erosions where vesicles have ruptured
  - Dermatomal distribution (does not cross midline)
  - Severe allodynia (pain to light touch)

### Workup and Results

**Clinical Diagnosis:**
- Classic presentation - laboratory confirmation not required

**If needed:**
- Tzanck smear: Multinucleated giant cells (positive)
- VZV PCR from vesicle fluid: Positive

### Clinical Image

![Herpes Zoster](case_01_image.jpg)

*Clinical photograph demonstrating herpes zoster with characteristic grouped vesicles on an erythematous base in a dermatomal distribution (T4-T5), stopping at the midline.*

### Diagnosis
**Herpes Zoster (Shingles) - Thoracic Dermatome**

Features:
- Reactivation of varicella-zoster virus from dorsal root ganglion
- Dermatomal, unilateral distribution
- Grouped vesicles on erythematous base

### Discussion
This case illustrates herpes zoster:

- **Dermatomal Distribution**: The lecture describes herpes zoster as having a dermatomal, unilateral distribution. The virus reactivates from the dorsal root ganglion where it has remained latent since primary varicella infection.

- **72-Hour Window**: The lecture emphasizes that treatment with antivirals is most effective when started within 72 hours of rash onset. This patient presented at day 3, still within the treatment window.

- **Tzanck Smear**: The lecture identifies the Tzanck smear as useful for rapid diagnosis of herpesvirus infections. It shows multinucleated giant cells but cannot distinguish HSV from VZV.

- **Grouped Vesicles**: The lecture describes the characteristic appearance of herpesviruses as grouped vesicles on an erythematous base.

### Treatment Plan
1. **Antiviral Therapy (within 72 hours):**
   - Valacyclovir 1000 mg three times daily for 7 days
   - OR Famciclovir 500 mg three times daily for 7 days
   - Reduces severity, duration, and risk of postherpetic neuralgia

2. **Pain Management:**
   - Acetaminophen and NSAIDs
   - Gabapentin or pregabalin for neuropathic pain
   - Opioids if needed for severe pain

3. **Wound Care:**
   - Keep lesions clean and dry
   - Calamine lotion for symptomatic relief
   - Avoid contact with immunocompromised individuals

4. **Monitoring:**
   - Watch for bacterial superinfection
   - Monitor for postherpetic neuralgia
   - Eye exam if facial involvement (herpes zoster ophthalmicus)

5. **Prevention:**
   - Recommend Shingrix vaccine after recovery (prevents recurrence)

### Teaching Points
1. Herpes zoster is dermatomal and unilateral (does not cross midline)
2. Antiviral treatment most effective if started within 72 hours
3. Tzanck smear shows multinucleated giant cells
4. Grouped vesicles on erythematous base are characteristic of herpesviruses
5. Postherpetic neuralgia is a major complication, especially in elderly

---

## Case 3: Tinea Capitis

### Patient Presentation
**Demographics:** 7-year-old male

**Chief Complaint:** Patchy hair loss and scalp itching for 3 weeks

**History of Present Illness:**
The patient's mother noticed areas of hair loss on his scalp 3 weeks ago. The areas have enlarged and become scaly. The child complains of itching. He has a pet cat at home. One classmate at school was recently diagnosed with a similar condition.

**Past Medical History:**
- No significant medical history

**Physical Examination:**
- Scalp:
  - Multiple circular patches of alopecia
  - "Black dot" appearance (broken hair shafts)
  - Scaling within the patches
  - Mild erythema
  - Posterior cervical lymphadenopathy
- No involvement of skin elsewhere

**Wood Lamp Examination:**
- Blue-green fluorescence in affected areas

### Workup and Results

**KOH Preparation:**
- Fungal hyphae visible within and around hair shafts (endothrix pattern)

**Fungal Culture:**
- Microsporum canis (consistent with cat exposure)

### Clinical Image

![Tinea Capitis](case_01_image.jpg)

*Clinical photograph showing tinea capitis with circular patches of alopecia, scaling, and the characteristic "black dot" appearance from broken hair shafts at the scalp surface.*

### Diagnosis
**Tinea Capitis - Microsporum canis**

Features:
- Dermatophyte infection of the scalp
- "Black dot" tinea from broken hair shafts
- Fluorescence under Wood lamp (Microsporum species)
- Requires oral antifungal therapy

### Discussion
This case illustrates tinea capitis:

- **Oral Antifungal Required**: The lecture emphasizes that tinea capitis requires oral antifungal therapy. Topical antifungals cannot penetrate the hair follicle adequately to clear infection.

- **Wood Lamp Fluorescence**: The lecture notes that Microsporum species fluoresce under Wood lamp examination. Most Trichophyton species do not fluoresce.

- **KOH Preparation**: The lecture identifies KOH preparation as the diagnostic test to identify fungal hyphae. It dissolves keratin and allows visualization of fungal elements.

- **Annular Plaques**: The lecture describes the classic appearance of dermatophyte infections (tinea corporis) as annular plaques with central clearing. In tinea capitis, the presentation is more commonly scaling alopecia.

### Treatment Plan
1. **Oral Antifungal Therapy:**
   - Griseofulvin 20-25 mg/kg/day (microsize) for 6-12 weeks
   - OR Terbinafine for 4-6 weeks (if Trichophyton)
   - Griseofulvin preferred for Microsporum

2. **Adjunctive Therapy:**
   - Selenium sulfide or ketoconazole shampoo 2-3 times/week
   - Reduces spore shedding (not sufficient alone)

3. **Prevention of Spread:**
   - Do not share combs, brushes, hats
   - Treat household contacts prophylactically
   - Evaluate and treat pet (veterinary referral)

4. **Monitoring:**
   - Clinical response in 2-4 weeks
   - Continue treatment until clinical and mycological cure
   - Repeat KOH or culture if no response

5. **School:**
   - May return to school once treatment initiated

### Teaching Points
1. Tinea capitis requires oral antifungal therapy (topicals insufficient)
2. KOH preparation identifies fungal hyphae
3. Microsporum species fluoresce under Wood lamp (not all dermatophytes do)
4. Griseofulvin is preferred for Microsporum; terbinafine for Trichophyton
5. Contact with animals (cats, dogs) is a common source

---

## Case 4: Scabies

### Patient Presentation
**Demographics:** 28-year-old female

**Chief Complaint:** Intense itching worse at night for 3 weeks

**History of Present Illness:**
The patient has had progressive, severe itching for 3 weeks. The itching is worse at night and interferes with sleep. She noticed small bumps on her wrists, between her fingers, and around her waist. Her boyfriend has developed similar symptoms. She works at a nursing home where several residents have been diagnosed with scabies.

**Physical Examination:**
- Skin:
  - Erythematous papules on wrists, finger web spaces, and waistline
  - Linear, thread-like **burrows** visible between fingers
  - Excoriations from scratching
  - No face or scalp involvement
  - Distribution: Wrists, web spaces, axillae, waist, genitalia

### Workup and Results

**Skin Scraping:**
- Mineral oil preparation: Sarcoptes scabiei mite, eggs, and fecal pellets (scybala) visualized

### Clinical Image

![Scabies](case_01_image.jpg)

*Clinical photograph showing scabies with characteristic linear burrows in the web spaces between fingers, along with erythematous papules. Burrows are pathognomonic for scabies infestation.*

### Diagnosis
**Scabies (Sarcoptes scabiei infestation)**

Features:
- Intense nocturnal pruritus
- Characteristic distribution (web spaces, wrists, waist, genitalia)
- Pathognomonic burrows
- Close contact transmission

### Discussion
This case illustrates scabies:

- **Mite Infestation**: The lecture identifies scabies as caused by the mite Sarcoptes scabiei, which burrows into the stratum corneum.

- **Burrows as Pathognomonic**: The lecture describes burrows as the pathognomonic finding in scabies. They represent the tunnels where female mites lay eggs.

- **Permethrin First-Line**: The lecture states that topical permethrin 5% is the first-line treatment for scabies. It is applied from neck to toes and left on for 8-14 hours.

- **Norwegian (Crusted) Scabies**: The lecture notes that Norwegian (crusted) scabies occurs in immunocompromised patients and is highly contagious due to massive mite burden.

### Treatment Plan
1. **Topical Permethrin 5% (First-Line):**
   - Apply to entire body from neck down
   - Include between fingers, under nails, genitalia
   - Leave on for 8-14 hours, then wash off
   - Repeat in 1 week

2. **Household Contacts:**
   - Treat all close contacts simultaneously
   - Even if asymptomatic

3. **Environmental Measures:**
   - Wash all clothing, towels, bedding in hot water
   - Items that cannot be washed: seal in plastic bag for 3 days
   - Vacuum furniture and carpets

4. **Pruritus Management:**
   - Antihistamines (diphenhydramine, hydroxyzine)
   - Pruritus may persist for 2-4 weeks after successful treatment (due to dead mite antigens)

5. **Alternative Treatment:**
   - Oral ivermectin 200 mcg/kg (repeat in 2 weeks)
   - Useful for outbreaks, crusted scabies, or treatment failure

### Teaching Points
1. Scabies is caused by the mite Sarcoptes scabiei
2. Burrows are pathognomonic
3. Permethrin 5% cream is first-line treatment
4. Treat all close contacts simultaneously
5. Norwegian (crusted) scabies is seen in immunocompromised patients

---

## Image Reference

For visual reference of skin infection concepts, see:
- Radiopaedia: [Necrotizing fasciitis](https://radiopaedia.org/articles/necrotizing-fasciitis) - Imaging findings
- Wikipedia: [Herpes zoster](https://en.wikipedia.org/wiki/Shingles) - Clinical features
- Radiopaedia: [Dermatophyte infection](https://radiopaedia.org/articles/dermatophyte-infection) - Overview

---

## Learning Points

1. **Necrotizing Fasciitis**: Pain out of proportion is the hallmark; urgent surgical debridement is critical

2. **Herpes Zoster**: Dermatomal, unilateral; antiviral within 72 hours; Tzanck shows multinucleated giant cells

3. **Tinea Capitis**: Requires oral antifungals; KOH shows hyphae; Microsporum fluoresces on Wood lamp

4. **Scabies**: Burrows are pathognomonic; permethrin 5% is first-line; treat all contacts