– Pyomyositis is an infection of the muscle, almost always due to Staphylococcus aureus. It most commonly affects the muscles of the limbs and torso. These infections may occur simultaneously in multiple sites.
– During the early indurated stage, while the muscle is swollen, hot and painful, medical treatment may be effective. During the suppurative stage, when the abscess has formed, surgical drainage is the only effective treatment.
– Immobilise the limb.
– Antibiotic therapy as for other abscesses (see Abscesses).
– Adapt analgesics to the pain level (see Pain, Chapter 1).
– Apply compresses soaked in 70% alcohol 2 times daily (max. 3 times daily to prevent burns to the skin).
Treatment of pyomyositis is by incision following the rules for incision of abscesses. Muscle abscesses are often deeper than other abscesses. As a result, needle aspiration with a large bore needle may be necessary to locate the abscess; it yields thick pus. Needle aspiration is insufficient treatment even if pus is evacuated.
Equipment and anaesthesia
As for abscesses.
– Generous incision along the axis of the limb, over the site of the abscess and avoiding underlying neurovascular stuctures; incise the skin, subcutaneous tissues and muscular fascia with a scalpel (Figure 11a).
– Dissect the muscle fibres with non-toothed forceps (Kelly type) or round tipped scissors. Insert the instrument into the muscle until the purulent cavity is reached. During insertion, keep the instrument closed and perpendicular to the muscle fibres. Withdraw gently with the scissors or forceps slightly open, keeping instrument perpendicular to the fibres (Figure 11b).
– Use a forefinger to explore the cavity, break down any loculi and evacuate the pus (Figure 11c).
– Wash abundantly with antiseptic solution.
– Insert a large drain.
– Fix the drain to the edge of the wound using a single suture. Remove the drain on about the 5th day (Figure 11d).
Figures 11: Surgical drainage of a pyomyositis
Myositis of the psoas muscle: if the abscess is on the right side, the clinical signs are the same as for appendicitis with pain in the right iliac area. Transfer the patient to a surgical centre.