Differential Diagnosis for Itchy Papular Rash on Shaft of Penis

• Single most likely diagnosis
  • Eczema/Dermatitis: This is a common condition that can cause itchy, papular rashes on the skin, including the genital area. The shaft of the penis is a typical location for irritant or allergic contact dermatitis.
• Other Likely diagnoses
  • Scabies: A parasitic infection caused by the mite Sarcoptes scabiei, which can lead to intense itching and papular rashes, often in the genital area.
  • Psoriasis: Although less common in the genital area, psoriasis can cause itchy, papular lesions and should be considered, especially if the patient has a history of psoriasis.
  • Lichen planus: An inflammatory condition that can affect the skin and mucous membranes, leading to itchy, papular rashes, which can occur on the genital area, including the penis.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Syphilis: The primary stage of syphilis can present with a painless, itchy papule or plaque (chancre) on the genitals, which is crucial to diagnose early due to its potential for serious complications if left untreated.
  • Genital herpes: Although typically associated with painful vesicles or ulcers, atypical presentations can occur, and it's essential to consider this diagnosis due to its implications for sexual health and the potential for severe complications.
• Rare diagnoses
  • Darier's disease: A rare genetic disorder that affects the skin, leading to itchy, papular rashes, which can occasionally involve the genital area.
  • Keratosis pilaris: A condition characterized by small, rough, sandpapery bumps on the skin, which can rarely occur on the penis and might cause itching.
  • Zinc deficiency: Can lead to skin lesions and rashes, including in the genital area, though this would be an uncommon presentation and typically associated with other systemic symptoms.