Fibromyalgia: This condition is characterized by widespread musculoskeletal pain, fatigue, and tender points. The pain can be exacerbated by cold weather, making it a likely diagnosis for patients experiencing muscular back and neck pain that worsens in cold conditions.

Muscle Strain: Cold weather can increase muscle stiffness and reduce flexibility, making muscle strains more likely. This could exacerbate existing back and neck pain.
Tendinitis: Similar to muscle strain, tendinitis (inflammation of the tendons) can be worsened by cold weather due to increased stiffness and reduced blood flow to the tendons.
Rheumatoid Arthritis: While not exclusively a muscular issue, rheumatoid arthritis can cause significant musculoskeletal pain that may worsen in cold weather due to increased stiffness and joint pain.
Hypothyroidism: Some patients with hypothyroidism may experience muscle aches and pains, including back and neck pain, which could potentially worsen in cold weather due to decreased metabolism and increased sensitivity to cold.

Spinal Stenosis: A condition where the spinal canal narrows, putting pressure on the spinal cord. While not directly related to cold weather, it's crucial to consider due to the potential for severe neurological consequences if left untreated.
Multiple Myeloma: A type of blood cancer that can cause bone pain, including back and neck pain. Cold weather might not directly exacerbate the pain, but the diagnosis is critical due to its severity and the need for prompt treatment.
Osteoporosis: Particularly in older adults, osteoporosis can lead to vertebral fractures, causing back pain. The risk of fracture might not be directly increased by cold weather, but the condition's presence can significantly impact the patient's quality of life and requires early detection.

Polymyalgia Rheumatica (PMR): An inflammatory disorder that causes muscle pain and stiffness, primarily in the shoulders and hips, but can also affect the neck and back. It's more common in older adults and can be exacerbated by cold weather.
Ehlers-Danlos Syndrome: A group of disorders that affect connective tissues supporting the skin, bones, blood vessels, and many other organs and tissues. Some types can cause significant musculoskeletal pain that might worsen in cold weather due to increased joint laxity and instability.
Cold Agglutinin Disease: A rare condition where the immune system produces antibodies that attack red blood cells at cold temperatures, potentially leading to pain and other symptoms if there's significant hemolysis (breakdown of red blood cells).