This is a disease of disadvantaged tropical communities in which abscesses form in a patient's muscles. It is common between the ages of 5 and 25, and becomes less common as living conditions improve.

There are several syndromes in which large collections of pus form in the muscles. The first is much the most common. You may see:

Classical pyomyositis in which one or more of a patient's muscles becomes exquisitely painful, tender, and swollen, and the skin over it smooth and shining. A single muscle may be involved, or a group of them, or he may have several abscesses in different parts of his body. His larger muscles, such as those of his thighs, buttocks, shoulders, back, and abdominal wall are more often involved than his smaller ones. Infection makes them hard and indurated, so that movement is painful. Later, the signs of inflammation may subside as the infected muscle is replaced by pus and becomes fluctuant. Infection of the muscle limits the movement of joints nearby. If his abscess is large, he may occasionally be quite ill with fever and rigors. Lymph node involvement is not conspicuous.

Septicaemia associated with pyomyositis may be fatal and is often not diagnosed. He is very ill and drowsy, with a high fever, and multiple tender areas over his muscles. He may have a history of a trivial skin laceration, a blister, or a small sore. The condition rapidly progresses, so that he becomes desperately ill with a swinging fever, weakness, prostration, dehydration and hypotension.

Pyaemia associated with pyomyositis results in a sequence of abscesses in one muscle after another.

Staphylococci are usually responsible. Before pus forms, antibiotics alone may occasionally cure him; but you almost always have to drain it.

SITA (38) presented with fever and a vague, mild pain in her left hip, which was made slightly worse by movement. No malaria parasites were found and no definite diagnosis was made. She was treated with gentamicin and cloxacillin and her fever improved. Ten days later she returned with a huge abscess in her left inguinal region. This was incised and she recovered completely. LESSON Pyomyositis may cause large abscesses in the deeper muscles with few localizing signs. Fig. 7-1 PYOMYOSITIS. A, shows an abscess in one of the muscles of a patient's thigh. B, the common sites. C, the distinction between pus in the muscles (as in pyomyositis), and pus between them, as in an abscess round a dead Guinea worm, which is one of the differential diagnoses. After Davey WW, ''Companion to Surgery in Africa', Figs. 11.2 and 11.5. Churchill Livingstone, with kind permission.

PYOMYOSITIS THE DIFFERENTIAL DIAGNOSIS includes osteomyelitis (7.2) and septic arthritis (7.16). The exact site of the tenderness and swelling will usually lead you to the correct diagnosis. There are several other possibilities which depend on the site of the abscess:

In the patient's upper abdomen, think of a kidney swelling, a perinephric abscess (5.11a), an amoebic liver abscess (31.12), a subphrenic abscess (6.4), or an acute abdomen.

In his lower abdomen, think of an appendix abscess, suppuration of his iliac glands (5.12), a psoas abscess, a strangulated inguinal hernia (14.6), or an acute abdomen.

In his loin, an inflammatory mass is more likely to be pyomyositis than a perinephric abscess or a pyonephros.

If he has an abscess in his iliopsoas, his hip is flexed, and he resists all attempts to straighten it (5.12). Careful comparison with his normal side may show a swelling medial to his anterior superior iliac spine. An iliac abscess (5.12) may be the result of pyomyositis of his iliacus or psoas muscle, suppurating iliac adenitis, osteomyelitis of his spine (7.15), or septic arthritis of his hip (7.18). Lightly banging his greater trochanter with your clenched fist will cause him pain if he has septic arthritis or osteomyelitis, but not in the other conditions. Examining his back should distinguish osteomyelitis. The distinction of pyomyositis from iliac adenitis may be impossible and is not important (5.12).

In his thigh, think of acute osteomyelitis, guinea worm infection, a haematoma, or a sarcoma.

In his calf think of a deep vein thrombosis, or a sickle cell crisis with bone infarction.

INVESTIGATIONS If osteomyelitis is a possibility, X- ray the part, but don't expect any changes for 10 days. Drill it (7.5). Measure his haemoglobin before you operate.

MANAGEMENT depends on the severity of his disease:

If his pyomyositis is early, in that there is merely induration over a small area of muscle, antibiotics alone may cure him. Give him penicillin, or chloramphenicol (2.7).

If he has one or more well localized lesions drain them.

If he has signs of spreading infection, give him antibiotics and drain the lesions.

If he has a succession of abcesses (pyaemia), drain them as they appear, culture the pus, and give him an appropriate antibiotic as soon as you know the results of culture. Give him chloramphenicol meanwhile.

If he is very ill indeed with multiple tender areas over his muscles, give him intraveous chloramphenicol (2.7). Change to oral chloramphenicol as he improves. Drain his abscesses.

If necessary, correct his dehydration with saline or Ringer's lactate. If he is severely anaemic, transfuse him before you drain his abscess.

DRAINAGE. Give him ketamine or a general anaesthetic. If you are not sure if pus is present or not, aspirate it with a needle.

Make a small incision to begin with, if possible in the most dependent position, and open his abscess by Hilton's method (5- 3). If it is large, extend the incision, so that you can insert your finger, break down any loculi and explore the whole cavity. Don't curette it. You may find a litre or more of pus.

If the bone feels rough and craggy at the bottom of the abscess cavity, it may be involved; if so, he has osteomyelitis, not pyomyositis.

DIFFICULTIES [s7]WITH PYOMYOSITIS If BLOOD POURS FROM THE ABSCESS, pack the cavity tightly with gauze for 36 hours. If you don't curette an abscess, it is unlikely to bleed much.

If he has very MANY or very SEVERE lesions, you may have to make 20 or more incisions, with repeated visits to the theatre, to evacuate pus and remove dead muscle.

If he has BLACK NECROTIC SKIN, removing it may reveal a huge quantity of avascular greyish-pink, mushy suppurating muscle extending deeply underneath. Remove this, taking care: (1) not to injure vital structures, (2) not to let him lose more blood than he can stand. His life depends on aggressive (but not too aggressive) surgery, intensive antibiotic treatment, and fluid replacement. Even so, he stands a good chance of dying. If you have had to remove much muscle, he will inevitably be left with weakness, deformity, and loss of function[md]a worthy price to pay for survival.

If he has FEVER and RIGORS after drainage, he is septicaemic, and may form new abscesses.

If he has any tendency to develop CONTRACTURES, apply skin traction (70.10) or a cast, as appropriate.

Fig. 7-2 THE PATHOLOGY OF OSTEOMYELITIS. A, Brodie's abscess is an uncommon form of chronic osteomyelitis: the upper end of the tibia or the lower femur are the common sites. B, the initial infection in osteomyelitis is typically in the metaphysis. After the age of 6 months the epiphyseal plates have developed sufficienty to prevent infection spreading to the joints, except in the hip. Before this age infection spreads to the joints. C, chronic osteomyelitis with sequestra and a sinus. D, under the age of 6 months osteomyelitis is always associated with septic arthritis. E, osteomyelitis of the proximal femur is always associated with septic arthritis, regardless of the age of the patient, because the epiphysial line is intracapsular.