Differential Diagnosis for Rash on Legs, Hands, and Fingernails

Single Most Likely Diagnosis

• Psoriasis: This condition is characterized by well-demarcated, erythematous, scaly plaques, which can appear on the legs, hands, and other parts of the body. The presence of small patches of white around fingernails and on the palm, known as pitting or nail psoriasis, further supports this diagnosis. The macular and papular rash, along with the diffuse and different-looking rash on hands, can also be seen in psoriasis due to its varied presentations.

Other Likely Diagnoses

• Eczema/Dermatitis: This condition can cause a macular and papular rash on the legs and hands, and it may also involve the fingers and palms. The appearance of small white patches could be related to lichenification or post-inflammatory hypopigmentation.
• Tinea Infections: Fungal infections like tinea pedis (athlete's foot) and tinea manuum (fungal infection of the hand) can cause a variety of rashes, including macular and papular types, and can lead to changes in skin coloration, including white patches.
• Pityriasis Rosea: Although less common on the hands, pityriasis rosea can cause a diffuse, macular, and papular rash on the body, including the legs, and sometimes involves the palms.

Do Not Miss Diagnoses

• Lupus Erythematosus: Systemic lupus erythematosus (SLE) can cause a wide range of skin manifestations, including a malar rash, discoid lupus, and photosensitivity, which might appear as a diffuse or macular rash on sun-exposed areas like the hands and legs. The presence of white patches could be related to discoid lupus or other manifestations.
• Scleroderma: This autoimmune disease can cause skin thickening and tightening, leading to changes in skin color and texture, including white patches due to sclerodactyly or calcinosis.
• Syphilis: Secondary syphilis can cause a wide range of skin manifestations, including macular, papular, and diffuse rashes on the palms and soles, which is a distinctive feature.

Rare Diagnoses

• Pityriasis Alba: A mild, chronic, eczematous condition that can cause hypo-pigmented patches, typically on the face but occasionally on other parts of the body, including the hands.
• Vitiligo: Characterized by the loss of pigment-producing cells (melanocytes), leading to white patches on the skin, which can appear anywhere, including around the fingernails and on the palms.
• Sarcoidosis: A systemic disease that can cause skin lesions, including macular and papular rashes, and can also involve the nails and lead to skin discoloration.