Dyshidrotic Eczema (Pompholyx): This condition is characterized by small, itchy blisters on the palms and soles, and sometimes the extensor surfaces of the hands. It's a common condition that matches the described localization and presentation.

Contact Dermatitis: This is a type of eczema caused by an allergic reaction or irritation from substances like soap, detergents, or certain metals. It can occur on any part of the body, including the palms and extensor surfaces of the hands, depending on the exposure.
Psoriasis: While psoriasis more commonly affects the elbows, knees, and scalp, it can also occur on the palms and soles. The extensor surfaces can be involved, especially in cases of psoriatic arthritis.
Palmar Psoriasis: A specific form of psoriasis that affects the palms, often presenting with thick, scaly plaques.

Secondary Syphilis: This condition can cause a rash on the palms and soles, which is a distinctive feature. Although less common, missing this diagnosis can have significant consequences due to the potential for neurological and cardiovascular complications if left untreated.
Lyme Disease: The rash of Lyme disease (erythema migrans) typically occurs at the site of the tick bite and can appear anywhere on the body, including the hands. While not exclusively localized to palms and extensor surfaces, its potential severity warrants consideration.

Keratoderma Blennorrhagicum: A rare condition associated with Reiter's syndrome (reactive arthritis), characterized by thickening of the skin on the palms and soles.
Pityriasis Rubra Pilaris: A rare skin disorder that can cause constant inflammation and scaling (exfoliation) of the skin, sometimes involving the palms and extensor surfaces.
Mycosis Fungoides: A type of cutaneous T-cell lymphoma that can present with various skin manifestations, including patches, plaques, or tumors on different parts of the body, including the hands, although this is less common.