The trunk is a large area that is host to a vast assortment of inflammatory, autoimmune, idiopathic, and neoplastic skin disorders. There are also many eruptions and symptoms that result from adverse drug reactions, infestations, as well as viral and bacterial infections.

Since the trunk is generally sun-protected by clothing, it is less likely to develop nonmelanoma skin cancers such as actinic keratoses, basal cell carcinomas, and squamous cell carcinomas; however, the back and anterior torso are common sites for melanoma to appear, particularly in men. (Since most of the infectious eruptions of the trunk occur in infants and children, Fever and Rash discusses them in Chapter 21.)



Notalgia Paresthetica

Nodulocystic Acne

Distinguishing Features

  • Nodules, cystic lesions, pustules (Fig. 11-3)

  • Healing with hypertrophic as well as atrophic scars

  • Abscesses and interconnecting sinuses may result

Hypertrophic Scar

Distinguishing Features

  • Elevated, firm, shiny, hairless, papules, or nodules; may be flesh-colored or tan

  • Lesions that are inflamed are usually of recent onset. They may be red or purple in color (Fig. 11-4)

  • Most often, they arise on the sternum (Fig. 11-5), the deltoid region of the upper arm, shoulders, and upper back

  • The most common sites on the head and neck are the earlobes, nasal alae, mandibular border, and posterior neck

  • Unlike keloids, the hypertrophic scar reaches a certain size and subsequently stabilizes or regresse, whereas keloids do not regress without treatment and tend to recur after excision


Distinguishing Features

  • Uncontrolled overgrowth of scar tissue with extension beyond the site of the original wound with a tendency to send out “claw-like” prolongations (Fig. 11-6)

  • Usually asymptomatic, although some are pruritic and others may be quite painful and tender

  • Keloids, by virtue of their excessive size, are generally of great cosmetic concern to patients

Adverse Drug Reactions

Common Examples of ADRs

Morbilliform reactions (measles-like) consist of blanchable red macules and papules that are seen predominantly on the trunk, thighs, upper arms, and face. Most often caused by sulfonamides, penicillin, aspirin, blood products, hydantoins, thiazide diuretics, allopurinol, quinidine, ACE inhibitors, barbiturates, carbamazepine, isoniazid, NSAIDs, and phenothiazines.

Distinguishing Features

  • Reactions often occur suddenly with or without fever and are often indistinguishable from viral exanthems

  • Lesions are pink, red, or purple in color (Fig. 11-9)

  • May become confluent in a symmetric, generalized distribution that often spares the face

  • Itching is common. The mucous membranes, palms, and soles may be involved

  • The onset occurs 7 to 10 days after starting the responsible drug, but sometimes may not appear until after the drug is discontinued

  • An eruption may last for 1 to 2 weeks and then fade

Acneiform eruptions generally appear on the trunk and are usually due to systemic steroids, topical steroids, lithium, and androgenic hormones.

Distinguishing Features

  • Lesions generally appear on the trunk as monomorphic acne-like papules and pustules (Fig. 11-10)

Contact dermatitis may be an irritant reaction from a topical tretinoin for acne or an allergic contact dermatitis from, e.g., topical neomycin or a preservative in a topical medication.

Photosensitive and phototoxic reactions are most commonly induced by phenothiazines, thiazide diuretics such as hydrochlorothiazide, griseofulvin, and doxycycline.

Distinguishing Features

  • Lesions appear in sun-exposed areas such as the “V” of the neck, upper sternum, extensor forearms, and the face as an exaggerated sunburn (Fig. 11-11)

Pruritus without a rash may be seen with ACE inhibitors.

Urticarial eruptions are most often caused by penicillin derivatives and sulfa drugs (see next section).

Diagnosis of Drug Eruptions

  • Obtaining a detailed, careful history is paramount

  • A drug-induced reaction should be considered in the differential diagnosis of any symmetric cutaneous eruption with sudden onset in a patient who takes medications

  • Skin biopsy of an exanthem showing perivascular lymphocytes and eosinophils may be helpful, but not diagnostic

  • Patch tests are useful in diagnosing allergic contact dermatitis (see Appendix: Diagnostic and Therapeutic Techniques)


Acute Urticaria

Distinguishing Features

  • Wheals are the color of the patient’s skin or appear pale red

  • Pruritus without excoriations

  • Annular or gyrate shapes (Fig. 11-12)

  • Individual lesions, by definition, last less than 24 hours (evanescent wheals)

  • Overall, acute urticarial episodes can last for days (generally less than 30 days)

  • Lesions may be accompanied by a deeper swelling (angioedema)

Chronic Urticaria

Distinguishing Features

  • The morphology and duration—less than 24 hours—of individual lesions is similar to that of acute urticaria; however, the condition, by definition, lasts for more than 6 weeks

  • Patients may also experience a coexistent physical urticaria such as dermatographism (see below)

  • Symptoms may continue for weeks, months, or years; however, in most cases the disease ends spontaneously

Clinical Variants

Physical urticaria is diagnosed by challenge testing. The following is a list of some of the physical urticarias and their causes:

  • Dermatographism (“skin writing”): urticaria that results from firm stroking or from scratching the skin. It can also be elicited by wearing tight garments (e.g., bras) (Fig. 11-13)

  • Cold urticaria: itchy hives occur at sites of cold exposure caused by cold winds or immersion in cold water

  • Solar urticaria: from sun exposure (Fig. 11-14, A and B)

  • Cholinergic urticaria: brought about by heat or exercise

Tinea Corporis

Distinguishing Features

  • Lesions often annular with peripheral enlargement and central clearing (Fig. 11-15)

  • Begins as a pruritic, circular or oval, erythematous, scaling patch or plaque that spreads centrifugally

  • Central clearing follows, while an active, advancing, raised border remains. The result is an annular (ring-shaped) plaque from which the disease derives its common name (“ringworm”)

  • Single or multiple lesions

  • May be pruritic or asymptomatic

Acute Lyme Disease

Distinguishing Features

Initial Phases

  • Initially, the LB lesion is a red macule or papule at the site of a tick bite. The bite itself usually goes unnoticed. Approximately 2 to 30 days after infection, the rash appears

  • Common sites are the trunk, groin, and thigh

  • Usually asymptomatic, the initial lesion expands to form an annular erythematous lesion, erythema migrans, which is the classic lesion of LB (Fig. 11-16)

  • Typically measures from 4 to 70 cm in diameter, generally with central clearing

  • The center of the lesion, which corresponds to the putative site of the tick bite, may become darker, vesicular, hemorrhagic, or necrotic

  • Lesions may be confluent (not annular), and concentric rings may form

  • Multiple lesions sometimes occur, likely the result of bacteremia (Fig. 11-17)

  • At the early stage of disease, flu-like symptoms, such as malaise, arthralgias, headaches, and a low-grade fever and chills, may develop

Intermediate, Chronic, and Late Phases

  • Some of the signs and symptoms of LB may not appear for weeks, months, or even years after the initial tick bite and are believed to be caused by immunopathogenic mechanisms. They include arthritis, nervous system problems, Bell palsy, headaches, memory loss, and cardiac dysrhythmias

  • Rarely, a lesion of lymphocytoma cutis or acrodermatitis chronica atrophicans appears

    • Late Lyme disease refers to symptoms, primarily rheumatologic and neurologic, that occur months to years after initial infection