Differential Diagnosis for Small Red Papules on Arms and Torso
Single Most Likely Diagnosis
- Guttae psoriasis: This condition is characterized by small, red, scaly papules that often appear on the arms, torso, and thighs. It's a common presentation, especially in children and young adults, and can be triggered by a streptococcal infection.
Other Likely Diagnoses
- Pityriasis rosea: Presents with small, red, scaly patches, often starting with a herald patch, followed by a widespread eruption. It typically affects the torso and proximal limbs.
- Eczema (atopic dermatitis): Can manifest as small, red, itchy papules, especially in individuals with a history of atopy. The distribution can vary but often involves the flexural areas, face, and neck, though it can spread to other areas including the arms and torso.
- Folliculitis: Inflammation of the hair follicles, which can appear as small, red bumps, often due to bacterial or fungal infections. It can occur anywhere on the body where hair is present.
Do Not Miss Diagnoses
- Meningococcemia: A severe infection caused by Neisseria meningitidis, which can present with a petechial or purpuric rash. Although the rash in meningococcemia is typically more severe and rapidly progressive, any sudden onset of a widespread rash, especially in a febrile patient, warrants immediate medical attention.
- Syphilis (secondary): Can cause a wide variety of skin manifestations, including small, red, papular lesions. The rash of secondary syphilis is often found on the palms and soles but can be widespread.
- Lymphoma (cutaneous T-cell lymphoma, e.g., mycosis fungoides): Although rare, cutaneous lymphomas can present with a variety of skin lesions, including small papules. The diagnosis is often delayed due to its rarity and nonspecific initial presentation.
Rare Diagnoses
- Papular urticaria: An itchy rash caused by an allergic reaction to insect bites, which can appear as small, red papules.
- Keratosis pilaris: A condition characterized by small, rough, sandpapery bumps, often on the arms, thighs, cheeks, and buttocks, due to keratin buildup in the hair follicles.
- Lichen nitidus: A rare condition presenting with tiny, shiny, flat-topped bumps, often on the arms, chest, abdomen, and genitals.