Hi, i'm a junior physio in northern ireland who has treated a lady with this condition.
Can be heriditary and aquired, my patient aquired it after excess alcohol and fall which resulted in may hours on the floor! Ultimately its muscle necrosis and a relase of muscle components into circulation and excretory system. Ethanol causes sarcolemmal injury leading to accumulation of Ca, crush injury/ischaemia also plays a significant role in muscular damage. The muscle disorder resolves in days/weeks due to regeneration of tissuse medically they will probably need dialysis and rehydration. Physio should inc respiratory care initially then rehab of muscle groups most affected with manual handling and progression of walking aids addressed also.
Hope this helps! Check out Rhabdomyolysis