A patient presents with a rash mostly on the arm, face, and hands, accompanied by fever. Based on this information, what disease is suspected?

The described symptoms—a rash primarily on the arms, face, and hands along with fever—are indicative of smallpox. Smallpox is characterized by a distinct rash that starts on the face and extremities and can become widespread, often accompanied by high fever. The type of rash seen in smallpox generally evolves into fluid-filled vesicles and then pustules, which is a key identifier for this disease.

While chickenpox, shingles, and measles may also present with rashes and fever, their distributions and symptoms differ. Chickenpox presents with a more generalized rash and is associated with pruritus, while shingles typically manifests as a localized rash and can be more painful due to its nerve involvement. Measles is marked by a more systemic presentation, including a koplik spots and a rash that usually begins at the hairline and moves downwards, which does not align with the description emphasizing the arms and face.

Thus, the combination of a fever and a rash specifically on the arms, face, and hands suggests smallpox as the most likely diagnosis.