Infectious diseases for MRCP Part 1

A 60-year-old man has 2 days of a spreading, hot, red, tender area over his left shin with a low-grade fever. There is a small area of athlete's foot between the toes. He is systemically well with normal observations. What is the most likely diagnosis?

1. Necrotising fasciitis A surgical emergency with pain far worse than the skin looks. Here, spreading hot red tender skin on one leg with a way in for the bacteria, otherwise well points elsewhere.
2. Contact dermatitis An inflamed rash from something the skin has touched. That does not match spreading hot red tender skin on one leg with a way in for the bacteria, otherwise well.
3. Cellulitis correct Correct. Spreading hot, red, tender skin on one leg with a way in for the bacteria is cellulitis.
4. Venous eczema or stasis dermatitis Often on both legs and itchy rather than infected. But spreading hot red tender skin on one leg with a way in for the bacteria, otherwise well does not point to it.
5. Deep abscess A pocket of pus that needs draining. It does not fit spreading hot red tender skin on one leg with a way in for the bacteria, otherwise well.

The point: Cellulitis is a sudden bacterial infection of the deeper layer of skin (dermis) and the fatty tissue underneath it, usually caused by Streptococcus pyogenes or Staphylococcus aureus. It shows up as a spreading area of hot, red, swollen and tender skin, most often on the lower leg, sometimes with fever and feeling generally unwell, and there is often a way in for the bacteria (a portal of entry) such as a break in the skin, athlete's foot (tinea pedis), an ulcer or lymph fluid swelling (lymphoedema). It is diagnosed by looking at it (a clinical diagnosis); the edge of the affected area is drawn on the skin to track whether it is spreading, and swabs are only taken if the skin is broken. First-choice treatment is flucloxacillin tablets, with clarithromycin or doxycycline for people allergic to penicillin, and admission for antibiotics into a vein if there are body-wide symptoms, fast spread, a weak immune system, or the tablets are not working. A grading system called the Eron classification helps decide where the patient should be treated. The important look-alikes are a blood clot in the leg (deep vein thrombosis, which can happen at the same time), venous eczema or stasis dermatitis (often on both legs and itchy rather than infected), and the emergency of necrotising fasciitis (a fast-spreading, deep infection that destroys tissue), which is suggested by pain far worse than the skin looks, fast spread, feeling very unwell all over, dead skin, or a crackling feeling under the skin (crepitus), and needs an urgent surgical opinion. Redness on both lower legs is rarely cellulitis and usually means venous disease instead. Cellulitis that keeps coming back in a limb with lymph fluid swelling may need long-term preventive antibiotics.

Source: NICE NG141 — cellulitis and erysipelas: antimicrobial prescribing NICE · tier 1, national regulator or guidance

A 60-year-old man has 2 days of a spreading, hot, red, tender area over his left shin with a low-grade fever. There is a small area of athlete's foot between the toes. He is systemically well with normal observations. What is the most appropriate investigation?

1. Doppler ultrasound if a deep vein thrombosis is suspected To rule out the look-alike. It does not fit spreading hot red tender skin on one leg with a way in for the bacteria, otherwise well.
2. Clinical assessment with marking of the area correct Correct. Cellulitis is diagnosed by looking at it, and marking the area tracks how it responds.
3. Swab only if the skin is broken Targets antibiotics when there is an open wound. Here, spreading hot red tender skin on one leg with a way in for the bacteria, otherwise well points elsewhere.
4. Urgent surgical assessment if necrotising fasciitis is possible For the emergency. But spreading hot red tender skin on one leg with a way in for the bacteria, otherwise well does not point to it.
5. Inflammatory markers and white cell count Support that it is an infection and show how severe it is. That does not match spreading hot red tender skin on one leg with a way in for the bacteria, otherwise well.

The point: Cellulitis is a sudden bacterial infection of the deeper layer of skin (dermis) and the fatty tissue underneath it, usually caused by Streptococcus pyogenes or Staphylococcus aureus. It shows up as a spreading area of hot, red, swollen and tender skin, most often on the lower leg, sometimes with fever and feeling generally unwell, and there is often a way in for the bacteria (a portal of entry) such as a break in the skin, athlete's foot (tinea pedis), an ulcer or lymph fluid swelling (lymphoedema). It is diagnosed by looking at it (a clinical diagnosis); the edge of the affected area is drawn on the skin to track whether it is spreading, and swabs are only taken if the skin is broken. First-choice treatment is flucloxacillin tablets, with clarithromycin or doxycycline for people allergic to penicillin, and admission for antibiotics into a vein if there are body-wide symptoms, fast spread, a weak immune system, or the tablets are not working. A grading system called the Eron classification helps decide where the patient should be treated. The important look-alikes are a blood clot in the leg (deep vein thrombosis, which can happen at the same time), venous eczema or stasis dermatitis (often on both legs and itchy rather than infected), and the emergency of necrotising fasciitis (a fast-spreading, deep infection that destroys tissue), which is suggested by pain far worse than the skin looks, fast spread, feeling very unwell all over, dead skin, or a crackling feeling under the skin (crepitus), and needs an urgent surgical opinion. Redness on both lower legs is rarely cellulitis and usually means venous disease instead. Cellulitis that keeps coming back in a limb with lymph fluid swelling may need long-term preventive antibiotics.

Source: NICE NG141 — cellulitis and erysipelas: antimicrobial prescribing NICE · tier 1, national regulator or guidance

A 60-year-old man has 2 days of a spreading, hot, red, tender area over his left shin with a low-grade fever. There is a small area of athlete's foot between the toes. He is systemically well with normal observations. What is the most appropriate management?

1. Clarithromycin or doxycycline for penicillin allergy An effective alternative. Here, spreading hot red tender skin on one leg with a way in for the bacteria, otherwise well points elsewhere.
2. Oral flucloxacillin first line correct Correct. Flucloxacillin tablets are the first choice for straightforward cellulitis in a patient who is otherwise well.
3. Urgent surgery for necrotising fasciitis The surgical emergency. It does not fit spreading hot red tender skin on one leg with a way in for the bacteria, otherwise well.
4. Intravenous antibiotics and admission for systemic or severe disease Guided by the Eron grading. But spreading hot red tender skin on one leg with a way in for the bacteria, otherwise well does not point to it.
5. Mark and review to confirm response To track whether it is spreading. That does not match spreading hot red tender skin on one leg with a way in for the bacteria, otherwise well.

The point: Cellulitis is a sudden bacterial infection of the deeper layer of skin (dermis) and the fatty tissue underneath it, usually caused by Streptococcus pyogenes or Staphylococcus aureus. It shows up as a spreading area of hot, red, swollen and tender skin, most often on the lower leg, sometimes with fever and feeling generally unwell, and there is often a way in for the bacteria (a portal of entry) such as a break in the skin, athlete's foot (tinea pedis), an ulcer or lymph fluid swelling (lymphoedema). It is diagnosed by looking at it (a clinical diagnosis); the edge of the affected area is drawn on the skin to track whether it is spreading, and swabs are only taken if the skin is broken. First-choice treatment is flucloxacillin tablets, with clarithromycin or doxycycline for people allergic to penicillin, and admission for antibiotics into a vein if there are body-wide symptoms, fast spread, a weak immune system, or the tablets are not working. A grading system called the Eron classification helps decide where the patient should be treated. The important look-alikes are a blood clot in the leg (deep vein thrombosis, which can happen at the same time), venous eczema or stasis dermatitis (often on both legs and itchy rather than infected), and the emergency of necrotising fasciitis (a fast-spreading, deep infection that destroys tissue), which is suggested by pain far worse than the skin looks, fast spread, feeling very unwell all over, dead skin, or a crackling feeling under the skin (crepitus), and needs an urgent surgical opinion. Redness on both lower legs is rarely cellulitis and usually means venous disease instead. Cellulitis that keeps coming back in a limb with lymph fluid swelling may need long-term preventive antibiotics.

Source: NICE NG141 — cellulitis and erysipelas: antimicrobial prescribing NICE · tier 1, national regulator or guidance