The trunk is a general term for the core body region including the chest, abdomen, flanks, and back. Excluding the V-neck and upper back, most of the trunk is covered by clothing, and thus is less exposed to sunlight. Therefore, photo-aggravated or photo-induced dermatoses can frequently be seen on the upper chest and upper back, but typically spare the rest of the trunk. On the other hand, the lower trunk is more commonly involved with dermatoses related to clothing. Clothing may incite rashes due to allergic contact dermatitis from chemicals in the clothing, soaps, dryer sheets, and laundry detergents. Clothing also may create a warmer, humid environment ideal for the development of diseases such as folliculitis, acne, and tinea versicolor.
A high density of sebaceous glands in the presternal area may provide an ideal location for malassezia yeast proliferation, making this a common location for seborrheic dermatitis.
Skin folds are also prominent on the trunk including the axilla as well as the infra-mammary and infra-abdominal regions. Skin folds are unique environments with increased moisture, due to sweat retention, and warmth, that breeds overgrowth of specific microbial flora, especially yeasts, and can lead to maceration. In addition, the occlusive environment increases various inflammatory pathways and can result in friction between tissues that can result in irritation. Finally, the umbilicus is unique in that it has a high density of apocrine glands. Interestingly, some conditions including psoriasis and scabies often favor this site.
Skin diseases involving the trunk can be broadly placed into the following categories starting with the most common diseases (Table 41-1):
Table 41-1.Skin diseases of the trunk. ||Download (.pdf) Table 41-1. Skin diseases of the trunk.
Allergic contact dermatitis (ACD)
F > M.
Age: Any age, may be more common in adults due to increased product usage.
Itchy rash, sometimes with blisters and painful fissures. Onset is hours to days after contact with allergen.
Geometric or linear configuration as well as a sharply demarcated distribution are clues to an external cause
Acute: Pink to red, edematous, plaques with papules and vesicles.
Chronic: Xerosis, fissuring, hyperpigmentation and lichenification at sites of direct contact with allergen.
Distinguish from other types of dermatitis due to a sharply demarcated distribution and geometric/linear configuration. Location is an important clue to the cause of ACD involving the axilla (e.g., preservatives, fragrances and clothing) or navel/lower abdomen (nickel).
(see Chapter 8).
Psoriasis vulgaris (chronic plaque psoriasis)
M = F.
Age: Any age but bimodal distribution peaks in 20s and 50s.
Asymptomatic to mildly pruritic. Chronic course. Associated with inflammatory arthritis and cardiovascular comorbidities (e.g., obesity, diabetes mellitus type II, ...