Pityriasis versicolor: A common fungal infection caused by Malassezia yeast, leading to hypopigmented or hyperpigmented patches on the skin, often on the trunk, but can also occur on the limbs. The appearance of white spots, especially if they are accompanied by fine scales, makes this a likely diagnosis.

Vitiligo: An autoimmune condition that causes the loss of pigment-producing cells (melanocytes), leading to white patches on the skin. It can occur anywhere on the body, including the lower limbs.
Idiopathic guttate hypomelanosis: A benign condition characterized by small, discrete, hypopigmented spots, often on the extremities, particularly in older adults or those with significant sun exposure.
Post-inflammatory hypopigmentation: This can occur after any inflammatory process of the skin, such as eczema, psoriasis, or dermatitis, where the inflammation leads to a temporary loss of skin pigmentation.

Tuberous sclerosis: A genetic disorder that can cause hypopigmented macules (ash leaf spots), which are often one of the earliest signs of the condition. These spots can appear anywhere on the body, including the lower limbs. Although rare, missing this diagnosis could have significant implications for the patient's health and family screening.
Neurofibromatosis type 1 (NF1): While more commonly associated with café-au-lait spots, NF1 can also present with hypopigmented patches. The condition has significant implications for the patient's health, including an increased risk of certain tumors.

Nevus depigmentosus: A rare, congenital condition characterized by a hypopigmented patch, usually present at birth or appearing in early childhood. It is a benign condition but can be mistaken for other, more serious conditions.
Waardenburg syndrome: A genetic disorder that can cause patches of hypopigmentation, among other symptoms like hearing loss and eye abnormalities. It's a rare condition but important to consider in the differential diagnosis of hypopigmented spots, especially if other systemic symptoms are present.