Strawberry eardrum: important sign of treatable acute otitis media

June 2004

A growing number of family physicians and pediatricians are recommending severely restricted use of antibiotics at the time of the initial diagnosis of acute otitis media (AOM). This recommendation is sometimes made without respect to the appearance of the tympanic membrane or the degree of pain from the infection. It may be appropriate to remind colleagues who advocate a nihilistic approach regarding antibiotic treatment of AOM of two “mean bugs” that invade the middle ear cleft and have a high potential for mesotympanic mischief. These are Streptococcus pyogenes and mucoid-appearing Streptococcus pneumoniae. Each of these, as well as other virulent strains of S. pneumoniae, can produce the appearance of a strawberry eardrum.

S. pyogenes

In the past 50 years, S. pyogenes (group A streptococcus) has been the causative bacteria for only 3% of cases of AOM in young children and a slightly higher percentage in older children and adolescents. Although S. pyogenes AOM is indeed uncommon, in the six-week period since March 1, 2004, we have obtained three middle ear cultures of this pathogen by culturing an acute otorrhea or by tympanocentesis, and two isolates of mucoid pneumococcus — very bad actors on the middle ear stage.

Prior to the widespread use of antibiotics, a substantial percentage of cases of AOM were caused by group A streptococci. Childhood exanthems, particularly measles, varicella and scarlet fever, were sometimes complicated by group A streptococci isolated from spontaneous otorrhea or from myringotomy specimens. S. pyogenes in the middle ear, protected from phagocytosis by its hyaluronic acid capsule, releases at least five streptococcal exoenzymes, such as streptokinase and DNAase B, that invoke an intense inflammatory response. This causes a child with group A streptococcal AOM to experience severe pain and protracted screaming. Group A streptococcal AOM also has a higher propensity to cause rupture of the thinned-out tympanic membrane (TM).

Left untreated by antibiotics, an estimated 10% of such infections progressed to acute mastoiditis; an unknown percentage progressed to necrotizing AOM with osteomyelitis and extensive damage to the middle ear ossicles and mucosa.

S. pneumoniae mucoid strains

S. pneumoniae usually appears as tiny checker-shaped colonies with a raised rim at the periphery and a tiny raised dot in the center of the colony. A narrow zone of alpha hemolysis surrounding the colony is seen on sheep blood agar plates. Occasionally, S. pneumoniae type 3 or 23 produces oily-appearing mucoid colonies because of an overproduction of hyaluronic acid in the capsule. These highly virulent, unique pneumococcal strains are capable of causing an exceptionally painful AOM. In such cases, the appearance of the TM is similar to that of group A strep.

Clinical signs and symptoms

S. pyogenes and mucoid pneumococcus usually present with an intensely painful earache invoking loud protracted crying or intractable screaming. These bad actors are the ones that force the child to continue to cry in the examining room. The appearance of the TM is characteristic: completely bulging, dark red and containing shaggy gray plaques of peeled-off, desquamated epithelial cells — strawberry TM. Often there is a visible transudate glistening on the surface of the angry-looking TM. The ear canal may have a semiliquid mixture of squamous debris and earwax; this material may seep out of the external auditory orifice and stain the child’s pillowcase or undershirt. The strawberry eardrum most often casts off its outer layer after resolution of the episode of AOM. The cast is an oval-shaped 10 mm by 11 mm layer of skin that is initially adjacent to and overlying the TM. Over the next few months, it migrates laterally, becomes coated with earwax in the outer third of the ear canal and is eventually extruded.

Initial office management

Should the ear canal have excess squamous debris, it may be cautiously suctioned or very gently syringed with warm water or saline to permit an unobstructed view of the TM. The thin, angry-looking TM with gray squamous plaques (strawberry TM) is then easily visualized. Sometimes these thinned-out TMs bulge more than halfway up the ear canal, and a gentle nick by a long sterile needle will provoke copious drainage of thin pus under pressure. It may be helpful to culture the child’s throat or nasopharynx when a strawberry TM is seen, because there is often a high concordance between group A strep in the oropharynx or nasopharynx and the same organism in the middle ear exudates. When the child presents with acute otorrhea after enduring hours of intense unremitting otalgia, a simple rapid antigen test for group A streptococcal antigen and overnight culture of the otorrhea fluid can quickly identify S. pyogenes or mucoid forms of S. pneumoniae. If S. pyogenes is detected in the draining middle ear exudate, a 10-day course of an appropriate anti-streptococcal antibiotic should be prescribed. Instillation of topical otic drops is not appropriate for treatment of streptococcal AOM.

Conclusion

Severe earache accompanied by a markedly bulging purple or dark red TM with shaggy gray-colored plaques of desquamated epithelium are the hallmarks of the strawberry TM. It should be clear that the clinical symptoms and classical signs of a strawberry eardrum mandate antibiotic treatment of AOM, irrespective of the age of the child.

For more information:

• Nielsen JC. “Studies on the Aetiology of Acute Otitis Media.” Copenhagen: Ejnar Mundsgaard Forlag; 1945. Classic work on preantibiotic etiology of acute otitis media with large section on streptococcal AOM.