Differential Diagnosis for Small Red Dots on Skin

Single Most Likely Diagnosis

• Petechiae or Purpura: These are small red or purple spots caused by bleeding under the skin, often due to minor trauma, vitamin deficiencies, or certain medications. Given the sudden appearance on multiple areas like arms, shoulders, and chest, this could be a likely explanation, especially if there's been any recent trauma or medication change.

Other Likely Diagnoses

• Allergic Reaction: An allergic reaction to a substance (like a new detergent, soap, or plant) could cause small red dots. This is plausible if the onset was sudden and there's been exposure to something new.
• Insect Bites: Multiple insect bites could present as small red dots, especially if the individual has been outdoors in areas prone to insect activity.
• Folliculitis: An inflammation of the hair follicles, often caused by bacterial or fungal infections, which could appear as small red dots, particularly if they are centered around hair follicles.
• Keratosis Pilaris: A harmless condition that causes small, rough, sandpaper-like bumps on the skin, which could be mistaken for red dots, especially if they become inflamed.

Do Not Miss Diagnoses

• Meningococcemia: A severe infection caused by Neisseria meningitidis, which can present with a petechial or purpuric rash. Although rare, it's critical to consider due to its high mortality rate if not promptly treated.
• Rocky Mountain Spotted Fever (RMSF): A bacterial infection spread by ticks, characterized by fever, headache, and a distinctive rash that can start as small red dots. Early diagnosis is crucial for effective treatment.
• Thrombocytopenia: A condition characterized by low platelet count, which can lead to petechiae or purpura. Identifying and treating the underlying cause is essential to prevent serious complications.

Rare Diagnoses

• Leukocytoclastic Vasculitis: A condition that involves inflammation of the blood vessels and can present with a rash of small red or purple spots. It's less common but should be considered if other symptoms like fever or joint pain are present.
• Schamberg's Disease: A rare condition causing progressive pigmentary purpura, which might initially appear as small red dots. It's chronic and benign but can be distressing due to its appearance.