I think that this is due to FMS being underdiagnosed in males. Flu-like achiness is frequently the most prominent symptom of FMS, but there are many others. For example, your eyes may be too dry, but at other times they will water. Your thermal regulatory system is out of whack. You may have to wait for your temperature to cool down after getting back in bed before you can pull the bedcover up.
Fingernails can break off, often in crescent-shaped pieces.
If nails do grow, they sometimes start to curve under. FMS is a sensitivity-amplification syndrome. This means that people with Fibromyalgia can be sensitive to smells, sounds, lights, odors, pressure and temperature fluctuations and vibrations. The noise emitted by fluorescent lights can drive you crazy. FMS sensitizes nerve endings as well as the rest of the autonomic nervous system, which means that the ends of the nerve receptors may have changed shape.