Differential Diagnosis for Rash Starting from Feet and Spreading Up

• Single Most Likely Diagnosis
  • Contact Dermatitis: This is a common condition that can start from the feet, especially if the patient has been exposed to an allergen or irritant, such as new shoes or certain chemicals in socks. The rash can spread upwards due to continued exposure or auto-eczematisation.
• Other Likely Diagnoses
  • Tinea Pedis (Athlete's Foot): A fungal infection of the foot that can spread up the legs if not treated. It's common in individuals who wear tight shoes, use public showers, or have poor foot hygiene.
  • Eczema (Atopic Dermatitis): Can start on the feet and spread upwards, especially in individuals with a history of atopy. It's characterized by itchy, inflamed skin.
  • Psoriasis: Although it typically starts on the elbows, knees, or scalp, psoriasis can begin on the feet and spread. It's known for well-delineated, red, scaly plaques.
• Do Not Miss Diagnoses
  • Meningococcemia: A life-threatening condition caused by Neisseria meningitidis. It can present with a rash that starts on the feet and spreads upwards, accompanied by fever, headache, and neck stiffness. Early recognition is crucial for survival.
  • Rocky Mountain Spotted Fever (RMSF): A tick-borne illness that can start with a rash on the feet and hands, then spread to other parts of the body. It's critical to diagnose early due to its high mortality rate if left untreated.
• Rare Diagnoses
  • Erythema Migrans (Lyme Disease): Typically presents as a single expanding lesion, but in rare cases, it can start on the feet. It's accompanied by other symptoms like fever, headache, and fatigue.
  • Kawasaki Disease: Although more common in children, it can present with a rash that starts on the feet and spreads, along with fever, conjunctivitis, and changes to the lips and mouth. It's a rare but important diagnosis due to its potential for cardiac complications.