More common in females with no evidence of family history, this syndrome is characterized by diffuse musculoskeletal pain, chronic fatigue, unrefreshed sleep, and increased tenderness in specific localized anatomic regions, but without laboratory evidence of contributing articular, non-articular, or metabolic disease. Patients complain of light sleep characterized by physical discomfort and awaken feeling tired and lethargic, with discomfort and stiffness in the joints.

The daytime tiredness and fatigue, at times with more specific complaints of excessive sleepiness, persist throughout the day. The muscles or groups of muscles are painful and tender, especially those of the neck and shoulder muscles. Particularly sensitive muscles and regions include the mid-upper border or the trapezius, the erector spinae muscle in the neck, the lateral sternal border over pectoralis major, just below the occipital crest, the lumbar erector spinae muscles, the lumbar triangle, the anterior superior spine, the mid-gluteus maximum, the mid-lateral thigh, and the medial knee superior to the adductor tubercle.

Minor trauma or changes in the weather, particularly cold or dampness, appear to exacerbate the muscle discomfort. Local heat and massage and anti-inflammatory agents often bring about some relief. Some patients with this syndrome have associated periodic limb movements. They are usually older and have a later onset of illness.

The chronicity and diffuseness of the symptoms often lead to a delayed diagnosis, resulting in features of an anxiety disorder or depression. The sleep complaints may be improved by specific treatment even though the muscle discomfort can persist.