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A 49-year-old man self-refers to dermatology for evaluation of new, painful nodules confined to his left axilla. He has never experienced anything like this, although he’s had the occasional “boil” on his legs and trunk in the past two years.
His medical history includes a coronary artery bypass three years ago and a recent follow-up arteriogram, performed in the hospital. It was shortly after this procedure that his axillary lesions appeared.
EXAMINATION
The patient is afebrile but in no distress. His fairly impressive lesions—red, fluctuant, and pus-filled—are confined to the left axilla. There are about 10, each averaging more than a centimeter in diameter. Each lesion is discrete, but none display a central comedone. The right axilla is unaffected.
One of the lesions is incised, releasing a modest amount of pus that is collected and submitted for bacterial culture. With a presumptive diagnosis of methicillin-resistant Staphylococcus aureus (MRSA), the patient is started on trimethoprim/sulfamethoxazole (double strength, bid for a month).
DISCUSSION
This case was clinically consistent with mild furunculosis caused by MRSA—an impression borne out by the bacterial culture and sensitivity. To be more precise, this patient had community-acquired MRSA (CA-MRSA), a relatively minor problem compared to more serious variants such as hospital-acquired MRSA; the latter usually requires hospitalization for delivery of IV antibiotics. (To further confuse the situation, I had to explain to the patient that, although he probably had CA-MRSA, he easily could have acquired it at the hospital where he had his arteriogram.)
The word boil is commonly used by the public to refer to almost any new, red, fluctuant mass. Inflamed epidermal cysts—which don’t usually involve infection—are classic examples of how the term is misused. But what the medical world terms a boil entails skin infection, and two common types of such lesions are furuncles and carbuncles.
Furuncles are red follicular pustules that develop around a hair. Usually of acute onset, furuncles are almost always bright red and often uncomfortable, if not painful. Staph, as in this case, is the most common cause, but not all furunculosis is associated with MRSA. More often, it is caused by relatively trivial normal flora, such as staph epidermidis, by pseudomonas (as in hot tub folliculitis), or even by a yeast-like fungus called Malassezia furfur. Bacterial culture is indicated when furunculosis is significant.
When furuncles coalesce, forming a single large, pus-filled mass in the skin, they are called carbuncles. Common on the neck, groin, and axillae, carbuncles are treated by liberating the contents (incision and drainage) and sometimes are packed to encourage continued drainage. Culture and sensitivity of the contents can guide rational treatment.
As far as the differential, cysts—even inflamed ones—can be of apocrine derivation, especially in the axillae. They can manifest singly or in multiples; one common condition, hidradenitis supprativa, manifests during puberty/menarche with multiple inflamed cysts in intertriginous (skin on skin) locations. There are typically multiple comedones on the surfaces of these lesions. Other types of cysts include pilar cysts (scalp), keratinous cysts (trunk and extremities), digital mucous cysts (fingers and occasionally toes), and ganglion cysts (overlying tendons).
Most cysts have organized, well-defined walls—a useful feature in distinguishing them from furuncles, carbuncles, and abscesses. The last are collections of pus usually associated with inflammation but not with hair follicles. As a result, they are able to form anywhere on the body (most notably, in the mouth). Some abscesses are sterile, such as those caused by heroin or medication injected accidentally into extravascular tissue. Incision and drainage, culture and sensitivity of the contents, and packing of the space are still indicated.
TAKE-HOME LEARNING POINTS
1) Furuncles are collections of pus associated with a hair follicle and are often caused by staph infection.
2) Carbuncles are composed of multiple furuncles that coalesce into a single larger pus-filled lesion, which is often called a “boil.”
3) MRSA is a form of furunculosis caused by Staphylococcus aureus.
4) Cysts can be inflamed but are almost never infected. Cysts have organized walls, a feature that helps distinguish them from furuncles and carbuncles.
5) Abscesses are collections of pus, often associated with inflammation but not with hair follicles.
6) Abscesses can be sterile, or they can be caused by anaerobic bacteria (eg, dental abscesses).
A 49-year-old man self-refers to dermatology for evaluation of new, painful nodules confined to his left axilla. He has never experienced anything like this, although he’s had the occasional “boil” on his legs and trunk in the past two years.
His medical history includes a coronary artery bypass three years ago and a recent follow-up arteriogram, performed in the hospital. It was shortly after this procedure that his axillary lesions appeared.
EXAMINATION
The patient is afebrile but in no distress. His fairly impressive lesions—red, fluctuant, and pus-filled—are confined to the left axilla. There are about 10, each averaging more than a centimeter in diameter. Each lesion is discrete, but none display a central comedone. The right axilla is unaffected.
One of the lesions is incised, releasing a modest amount of pus that is collected and submitted for bacterial culture. With a presumptive diagnosis of methicillin-resistant Staphylococcus aureus (MRSA), the patient is started on trimethoprim/sulfamethoxazole (double strength, bid for a month).
DISCUSSION
This case was clinically consistent with mild furunculosis caused by MRSA—an impression borne out by the bacterial culture and sensitivity. To be more precise, this patient had community-acquired MRSA (CA-MRSA), a relatively minor problem compared to more serious variants such as hospital-acquired MRSA; the latter usually requires hospitalization for delivery of IV antibiotics. (To further confuse the situation, I had to explain to the patient that, although he probably had CA-MRSA, he easily could have acquired it at the hospital where he had his arteriogram.)
The word boil is commonly used by the public to refer to almost any new, red, fluctuant mass. Inflamed epidermal cysts—which don’t usually involve infection—are classic examples of how the term is misused. But what the medical world terms a boil entails skin infection, and two common types of such lesions are furuncles and carbuncles.
Furuncles are red follicular pustules that develop around a hair. Usually of acute onset, furuncles are almost always bright red and often uncomfortable, if not painful. Staph, as in this case, is the most common cause, but not all furunculosis is associated with MRSA. More often, it is caused by relatively trivial normal flora, such as staph epidermidis, by pseudomonas (as in hot tub folliculitis), or even by a yeast-like fungus called Malassezia furfur. Bacterial culture is indicated when furunculosis is significant.
When furuncles coalesce, forming a single large, pus-filled mass in the skin, they are called carbuncles. Common on the neck, groin, and axillae, carbuncles are treated by liberating the contents (incision and drainage) and sometimes are packed to encourage continued drainage. Culture and sensitivity of the contents can guide rational treatment.
As far as the differential, cysts—even inflamed ones—can be of apocrine derivation, especially in the axillae. They can manifest singly or in multiples; one common condition, hidradenitis supprativa, manifests during puberty/menarche with multiple inflamed cysts in intertriginous (skin on skin) locations. There are typically multiple comedones on the surfaces of these lesions. Other types of cysts include pilar cysts (scalp), keratinous cysts (trunk and extremities), digital mucous cysts (fingers and occasionally toes), and ganglion cysts (overlying tendons).
Most cysts have organized, well-defined walls—a useful feature in distinguishing them from furuncles, carbuncles, and abscesses. The last are collections of pus usually associated with inflammation but not with hair follicles. As a result, they are able to form anywhere on the body (most notably, in the mouth). Some abscesses are sterile, such as those caused by heroin or medication injected accidentally into extravascular tissue. Incision and drainage, culture and sensitivity of the contents, and packing of the space are still indicated.
TAKE-HOME LEARNING POINTS
1) Furuncles are collections of pus associated with a hair follicle and are often caused by staph infection.
2) Carbuncles are composed of multiple furuncles that coalesce into a single larger pus-filled lesion, which is often called a “boil.”
3) MRSA is a form of furunculosis caused by Staphylococcus aureus.
4) Cysts can be inflamed but are almost never infected. Cysts have organized walls, a feature that helps distinguish them from furuncles and carbuncles.
5) Abscesses are collections of pus, often associated with inflammation but not with hair follicles.
6) Abscesses can be sterile, or they can be caused by anaerobic bacteria (eg, dental abscesses).
A 49-year-old man self-refers to dermatology for evaluation of new, painful nodules confined to his left axilla. He has never experienced anything like this, although he’s had the occasional “boil” on his legs and trunk in the past two years.
His medical history includes a coronary artery bypass three years ago and a recent follow-up arteriogram, performed in the hospital. It was shortly after this procedure that his axillary lesions appeared.
EXAMINATION
The patient is afebrile but in no distress. His fairly impressive lesions—red, fluctuant, and pus-filled—are confined to the left axilla. There are about 10, each averaging more than a centimeter in diameter. Each lesion is discrete, but none display a central comedone. The right axilla is unaffected.
One of the lesions is incised, releasing a modest amount of pus that is collected and submitted for bacterial culture. With a presumptive diagnosis of methicillin-resistant Staphylococcus aureus (MRSA), the patient is started on trimethoprim/sulfamethoxazole (double strength, bid for a month).
DISCUSSION
This case was clinically consistent with mild furunculosis caused by MRSA—an impression borne out by the bacterial culture and sensitivity. To be more precise, this patient had community-acquired MRSA (CA-MRSA), a relatively minor problem compared to more serious variants such as hospital-acquired MRSA; the latter usually requires hospitalization for delivery of IV antibiotics. (To further confuse the situation, I had to explain to the patient that, although he probably had CA-MRSA, he easily could have acquired it at the hospital where he had his arteriogram.)
The word boil is commonly used by the public to refer to almost any new, red, fluctuant mass. Inflamed epidermal cysts—which don’t usually involve infection—are classic examples of how the term is misused. But what the medical world terms a boil entails skin infection, and two common types of such lesions are furuncles and carbuncles.
Furuncles are red follicular pustules that develop around a hair. Usually of acute onset, furuncles are almost always bright red and often uncomfortable, if not painful. Staph, as in this case, is the most common cause, but not all furunculosis is associated with MRSA. More often, it is caused by relatively trivial normal flora, such as staph epidermidis, by pseudomonas (as in hot tub folliculitis), or even by a yeast-like fungus called Malassezia furfur. Bacterial culture is indicated when furunculosis is significant.
When furuncles coalesce, forming a single large, pus-filled mass in the skin, they are called carbuncles. Common on the neck, groin, and axillae, carbuncles are treated by liberating the contents (incision and drainage) and sometimes are packed to encourage continued drainage. Culture and sensitivity of the contents can guide rational treatment.
As far as the differential, cysts—even inflamed ones—can be of apocrine derivation, especially in the axillae. They can manifest singly or in multiples; one common condition, hidradenitis supprativa, manifests during puberty/menarche with multiple inflamed cysts in intertriginous (skin on skin) locations. There are typically multiple comedones on the surfaces of these lesions. Other types of cysts include pilar cysts (scalp), keratinous cysts (trunk and extremities), digital mucous cysts (fingers and occasionally toes), and ganglion cysts (overlying tendons).
Most cysts have organized, well-defined walls—a useful feature in distinguishing them from furuncles, carbuncles, and abscesses. The last are collections of pus usually associated with inflammation but not with hair follicles. As a result, they are able to form anywhere on the body (most notably, in the mouth). Some abscesses are sterile, such as those caused by heroin or medication injected accidentally into extravascular tissue. Incision and drainage, culture and sensitivity of the contents, and packing of the space are still indicated.
TAKE-HOME LEARNING POINTS
1) Furuncles are collections of pus associated with a hair follicle and are often caused by staph infection.
2) Carbuncles are composed of multiple furuncles that coalesce into a single larger pus-filled lesion, which is often called a “boil.”
3) MRSA is a form of furunculosis caused by Staphylococcus aureus.
4) Cysts can be inflamed but are almost never infected. Cysts have organized walls, a feature that helps distinguish them from furuncles and carbuncles.
5) Abscesses are collections of pus, often associated with inflammation but not with hair follicles.
6) Abscesses can be sterile, or they can be caused by anaerobic bacteria (eg, dental abscesses).
