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CASE REPORT
Primary pyomyositis in an infant following one-day afebrile
upper limb monoplegia
Yusuke Takezawa, Soh Niitsuma, Sayaka Kawashima, Shunsuke Miyano, and Takashi Honma
Department of Pediatrics, Ishinomaki Red Cross Hospital, Ishinomaki, Miyagi, Japan

Abstract : Background : Pyomyositis is a subacute bacterial infection of the skeletal muscles. Its most commonfeatures are fever, muscle swelling, and focal pain. There have been insufficient data regarding pyomyositis in
healthy infants. Case report : A one-month-old boy presented with an impairment of his left arm movement. Hewas well-nourished and not under any apparent distress. His vital signs were within the normal limits but neurological examination revealed left forearm paralysis. Physical examination showed no abnormal findings in theregion from the left shoulder joint to the fingertips. Considering these factors, an intracranial pathology was initially suspected. However, he developed a fever, regular tachycardia, and swelling in the left forearm. Magnetic
resonance imaging revealed inflammation in the left forearm muscles. He was diagnosed with bacterial myositis
and started on intravenous antibiotics. On the 17th day, he was discharged with oral antibiotic treatment, which
was completed over 25 days without any sequelae nor relapse. Conclusion : Here we report the case of Japanese
primary pyomyositis following one-day afebrile upper limb monoplegia in an infant. Even when infants exhibit
afebrile symptoms, a bacterial infection should be suspected. J. Med. Invest. 68 : 372-375, August, 2021
Keywords : bacteremia, immunocompetence, paralysis, soft tissue infection, Staphylococcus aureus

INTRODUCTION
Pyomyositis is a subacute bacterial infection of the skeletal
muscles ; it had been originally reported as tropical pyomyositis
in tropical areas (1). It commonly afflicts immunocompromisedor elderly people in temperate climate areas, whereas healthy
children and young adults have reportedly been afflicted inareas with a tropical climate (2, 3). Pyomyositis is mostly causedby Staphylococcus aureus, and typical pyomyositis symptoms include fever, muscle swelling, and focal pain (2). To date, manycase reports on pyomyositis have been published ; however, there
are insufficient data on cases of pyomyositis in children, especially healthy infants. Here we report the case of a one-month-oldbaby with left forearm pyomyositis following one-day afebrile
upper limb monoplegia of the left upper limb.

CASE REPORT
A 1-month-old boy presented to the emergency department
with his mother complaining of no movement in his left arm.
Otherwise, the patient was apparently healthy and even-tempered, and his physical examination findings were normal.
He was re-examined in the pediatric department the next
day of the first visit. He was the third child born to a healthy,
non-consanguineous Japanese couple. He had neither remarkable history of injury, severe infection, nor perinatal event. His
general examination findings were as follows : temperature,
36.8°C ; pulse rate, 140 / min ; respiratory rate, 30 / min ; andsaturation of peripheral oxygen, 99% (room air). His body weightwas 4.6 kg ; he appeared well-nourished, and was not under any
Received for publication December 7, 2020 ; accepted March 14, 2021.
Address correspondence and reprint requests to Yusuke Takezawa,
M.D., Ph.D., Department of Pediatrics, Tohoku University Schoolof Medicine, 2-1 Seiryo-machi, Aoba-ku, Sendai, Miyagi 980-8574,
Japan and Fax : +81-22-717-7290.

apparent distress. Neurological examination revealed a movement impairment of his left arm, with only slight movement
observed on eliciting Moro or grasp reflex. Physical inspection
and palpation of the left arm showed no apparent findings in theregion from the shoulder joint to the fingertips and caused noapparent irritability or cry. His left arm radiographs revealed
no abnormality. Blood test results showed a total white blood
cell count of 19,200 / μl and slightly increased C-reactive protein
levels (1.2 mg / dl). Venous blood gas analysis, blood electrolyte
levels, and renal function test parameters were within thenormal limits. He was admitted to the hospital for monitoring
and further examination. An intracranial pathology, including
cerebral hemorrhage, was suspected at the time of admission
despite the absence of hyperreflexia since no other apparent
etiology could be identified based on his clinical presentations.
However, almost 24 hours after the onset of symptoms, he developed regular tachycardia (up to 190 beats / min) and swelling in
the left forearm. Magnetic resonance imaging (MRI) for the left
forearm was performed to verify a possible local infection suchas osteomyelitis. MRI findings revealed inflammation in theleft forearm muscles (Fig. 1-A, B). Intravenous administrationof ampicillin / sulbactam (150 mg / kg / day q6h) and clindamycin(40 mg / kg / day q12h) was initiated. After initiating antibiotictreatment, the patient’s body temperature increased to 39°C but
he became afebrile within 3 days. His blood culture was positive
for methicillin-susceptible S. aureus, following which cefazolin(100 mg / kg / day) monotherapy was initiated. Ultrasonographyof the left arm on the fifth day of admission showed consolidationand swelling in the left forearm muscles ; these image findings
eventually disappeared on the 15th day of admission (Fig. 1-C,D). On the fourth day of admission, he began to move his leftarm, and the swelling began to subside between the fourth andeighth days ; both the symptoms were eventually resolved. Onthe 11th day, the flexion attitude of his elbow and shoulder haddisappeared. On the 15th day, the patient’s blood test results
revealed that the inflammation had completely subsided. On the17th day, he was discharged with oral cefdinir (18 mg / kg / day)treatment. The antibiotic treatment and his follow-up continued

The Journal of Medical Investigation Vol. 68 2021

The Journal of Medical Investigation Vol. 68 August 2021
for a period of 24 days without relapse. During the one-weekfollow-up period after the discharge, the patient had been symptom-free without any sequelae, including his left arm movement.
The patient’s clinical course is summarized in Fig. 2. Ultrasonography of his spleen revealed no dysplastic abnormalities. His
blood cell count and hemogram were normal. Furthermore, his
immunoglobulin and complement levels were within the normal

373

range (IgG, 1683 mg / dl ; IgA, 84 mg / dl ; IgM, 159 mg / dl ; IgG4,27 mg / dl ; CH50, 24.2 / ml ; C3, 116 mg / dl ; and C4, 16 mg / dl).
Subsequent immunological examination was not performed as
the patient responded well to the treatment and there was noabscess formation or requirement of surgery. Informed consent
was obtained from the parents.

Fig 1. Magnetic resonance imaging (MRI) and ultrasonography (US) images ofthe patient’s left forearm. (A) Contrast-enhanced MRI of the left forearm using T1weighted sagittal imaging. (B) Contrast-enhanced MRI of the left forearm using T2weighted coronal imaging. (C, D) US imaging of the right (C) and left (D) forearmFig 2. Clinical course of the patientY. Takezawa, et al. Primary pyomyositis in an infant374
DISCUSSION

This study reported the first case of Japanese primary pyomyositis in infancy following one-day afebrile upper limb
monoplegia. The patient’s left arm function seemed to be completely restored without any surgical intervention ; however,symptoms were atypical, and nearly 24 h were required to makea diagnosis.
Although some reports on pyomyositis cases have been published, cases in infants have not yet been reported in Japan.
A comparison of the reported pediatric primary pyomyositis
cases (including cases in infants) is presented in Table 1 (4-7).
Considering these references, this disease tends to affect thetruncal or lower limb muscles, and the most common symptoms
include fever, muscle pain, swelling, and a feeling of warmth. Inaddition, infant cases of pyomyositis are rare. Therefore, our casewas relatively unusual in terms of the patient’s age, site involved,and symptoms. In fact, a few infant cases have reported to show
the impairment of muscle movements, but these cases simultaneously showed other symptoms including fever, pain, or swelling (8, 9). Our patient exhibited the impairment of the left arm
movement without any other symptoms for almost 24 hours fromonset. When infants have bacterial infections, they occasionallyshow afebrile symptoms (e.g., lethargy or irritability) (10). In thepresent case, the patient had the impairment of left arm movement without not only fever or local findings but also lethargy
or irritability, which made the diagnosis tricky. Also, he did notshow any preceding history or trauma ; therefore, it was difficult
to determine whether the left arm muscle was the primary causeof concern or was it a sequela of infections such as septicemia. In
terms of the cause of monoplegia, it was undetermined whether
the secondary peripheral motor nerve paralysis due to inflammation or myositis itself caused muscular dysfunction because aneurophysiological examination was not performed.

Table 1. Comparison of the clinical features of pediatric patients with primary pyomyositis
Citation
Country

Present case

Emmanuel(1999)

Pia et al.
(2006)

Chiu et al.
(2009)

Unnikrishnan
et al. (2010)

JapanNigeriaUSTaiwan

UKNo. of patients

131452413Male, n (%)

1 (-)

15 (48)31 (69)13 (54)7 (54)

Age, range (year)

0.1

0–15

0.1–15

0.1–15

4–15

Fever+ (delayed)

1042

20

13Swelling+ (delayed)

3126

8N/D

Local pain+ (delayed)

3145

5N/D

Paralysis

+

−

−−

N/D

Symptoms

Pathogens
MSSA+

16*

101010

MRSA

−

−

164−

Other GPC

−

2*

13

1

GNRs

−

−−

2−

GNC−

−

−

1−

Unknown

−

1518

42+

4

12−

§Site

Upper limbs
Lower limbs−

1824144

Truncus−9872

Buttock−

01327−43−−

Therapy duration

24 days

N/DN/D

2–7 weeks

3–6 weeks

Days before present

1

2–12

N/D

N/D

3–211

†15Others

Comorbidity

None0MSSA, methicillin-sensitive Staphylococcus aureus ; MRSA, methicillin-resistant Staphylococcus aureus ; GPC, grampositive cocci. ; GNRs, gram-negative rods ; GNC, gram-negative cocci.; +, present ; −, absent ; N / D, no data ; §, including
multifocal site ; *, including multi-pathogen ; †, excluded with this study

The Journal of Medical Investigation Vol. 68 August 2021
CONCLUSION
Here we report the case of Japanese primary pyomyositis
following one-day afebrile upper limb monoplegia in an infant.
When infants exhibit afebrile symptoms without any causative
history, bacterial infection should be suspected.

CONFLICT OF INTERESTS
The authors declare no conflict of interest.

ACKNOWLEDGEMENTS
The authors would like to thank the patient and his family
and the medical staff who participated in the patient’s care. The
authors declare no conflict of interest. Also, no funding was received that could influence this article.

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