Subacute Cutaneous Lupus Erythematosus (SCLE): This condition is characterized by the presence of erythematous, round, scaling papules, particularly on sun-exposed areas such as the cheeks, nose, and chest. The patient's flu-like symptoms, low-grade fever, malaise, and the involvement of bilateral knees, elbows, and wrists with erythema and tenderness are also consistent with SCLE, which is a subtype of lupus erythematosus.

Psoriasis: The scaling papules and the distribution of the rash could suggest psoriasis, especially given the involvement of the elbows and knees. However, the presence of systemic symptoms like low-grade fever and malaise, along with the specific pattern of the rash, makes SCLE more likely.
Dermatomyositis: This condition is characterized by skin manifestations (such as a heliotrope rash on the face and erythema on the knuckles, knees, elbows, and feet) and muscle weakness. While the patient's rash and joint involvement could suggest dermatomyositis, the absence of reported muscle weakness makes it less likely.
Seborrheic Dermatitis: This condition can cause erythematous, scaling lesions on the face, particularly in a "butterfly" distribution across the nose and cheeks. However, it typically spares the chest, neck, and joints, making it less likely in this case.

Systemic Lupus Erythematosus (SLE): While SCLE is a subtype of lupus, SLE itself is a more severe condition that can affect multiple organ systems. The patient's systemic symptoms could be indicative of SLE, which would require immediate attention due to its potential for serious complications.
Lymphoma: Certain types of lymphoma, such as cutaneous T-cell lymphoma, can present with skin lesions and systemic symptoms. Although less likely, missing a diagnosis of lymphoma could have severe consequences.
Infectious Diseases (e.g., Lyme Disease, Syphilis): These conditions can present with a wide range of symptoms, including rashes and systemic illness. They are important to consider due to their potential for serious complications if left untreated.

Sarcoidosis: This condition can cause skin lesions, joint symptoms, and systemic illness. While it is less common, its presentation can be varied, making it a consideration in cases with multiple systemic symptoms and skin findings.
Erythema Multiforme: This is an immune-mediated condition that can cause target-like lesions on the skin and sometimes involves the mucous membranes. It is often triggered by infections or medications and can be severe, but the description provided does not closely match the typical presentation of erythema multiforme.