Trichomycosis (trichobacteriosis)

INTRODUCTION — Trichomycosis is a superficial bacterial infection of hair that is also known more appropriately as trichobacteriosis. The primary causative agents are Corynebacterium species (usually Corynebacterium flavescens).

Trichomycosis presents with yellow-white (occasionally red or black), soft, malodorous nodules and sheath-like structures on hair shafts (picture 1A-C). The infection most often affects the axillary hair (trichomycosis axillaris) but can also involve other sites, such as pubic (trichomycosis pubis), scrotal, and intergluteal hair.

The clinical features, diagnosis, and management of trichomycosis will be reviewed here. Trichomycosis should be distinguished from other disorders that present with nodules on hair shafts, such as piedra and pediculosis (table 1). These disorders are reviewed separately. (See "Piedra" and "Infections due to Trichosporon species and Blastoschizomyces capitatus (Saprochaete capitata)", section on 'Superficial infection' and "Pediculosis pubis and pediculosis ciliaris" and "Pediculosis capitis".)

MICROBIOLOGY — Trichomycosis typically results from infection with Corynebacterium spp, which are gram-positive and rod-shaped bacteria. Examples of identified species include C. flavescens (most common) and Corynebacterium propinquum [1,2]. Dermabacter hominis has also been reported to cause trichomycosis [3].

EPIDEMIOLOGY AND RISK FACTORS — Trichomycosis is a relatively common but under-recognized condition.

●Age and sex – Trichomycosis is most often diagnosed in adolescent and young adult males but may also occur in females and at any age, including infancy [4]. The lower incidence in females may be related to a higher prevalence of axillary shaving. In a retrospective study in Mexico City, 53 of 56 patients (95 percent) with clinically and microbiologically confirmed trichomycosis were males, with the average age being 32.5 years [1].

●Predisposing factors – Poor hygiene, hyperhidrosis, obesity, and high humidity are predisposing factors [1,4-6]. The infection tends to be more prevalent in humid and tropical climates than in temperate climates.

●Transmission – Person-to-person transmission has been reported but is not considered a major mode of transmission. It is most likely to occur in groups that live in close quarters, such as soldiers and athletes [1].

PATHOGENESIS — Infection is limited to the free hair shaft; the hair root and follicle are unaffected. The nodules and sheath-like structures surrounding hairs contain high numbers of bacteria and are postulated to result from a combination of dried and hardened apocrine sweat, proliferating corynebacteria, and bacterial products. The associated odor may be partially due to bacterial metabolism of testosterone in apocrine sweat into malodorous compounds.

The occurrence of red and black, sheath-like structures in the trichomycosis rubra and trichomycosis nigra clinical variants may result from symbiosis with chromogenic bacteria. Examples include Micrococcus castellani, Micrococcus nigricans, and Serratia marcescens [1,7]. (See 'Clinical presentation' below.)

CLINICAL PRESENTATION

●Appearance – Trichomycosis is characterized by creamy, opaque, soft-in-consistency, and easily scraped-off nodules and sheath-like structures on the hair shaft (picture 1A-C) [1]. The structures are typically yellow-white (trichomycosis flava). Less frequently, the structures are red (trichomycosis rubra) or black (trichomycosis nigra). (See 'Pathogenesis' above.)

●Location – Axillary hair is the most common site for trichomycosis [1]. Less common sites include pubic (trichomycosis pubis) and intergluteal hair, and there are rare reports of eyebrow and scalp hair involvement [1,8]. Eyebrow involvement was attributed to autoinoculation from axillary hair [1].

●Course – Early infection may be more easily palpated as irregular thickening of the hair shaft than visualized. As infection progresses, the deposits become more visible and extend along the entire length of the hair shaft, forming a sheath and causing the hair to appear thickened [1].

●Associated findings – Sweaty, malodorous axillae with a rancid, acidic odor are common. Symptoms, such as pruritus or pain, are generally absent.

ASSOCIATED DISORDERS — Trichomycosis often occurs in association with hyperhidrosis. Trichomycosis pubis is also linked with poor hygiene and obesity [9].

In addition, patients may have concomitant cutaneous corynebacterial infections, including erythrasma and pitted keratolysis [1,10,11]. A study of a cohort of 108 male Korean soldiers with pitted keratolysis found 22 (20 percent) with concomitant physical findings consistent with trichomycosis axillaris and 14 (13 percent) with both trichomycosis axillaris and erythrasma [10]. (See "Erythrasma" and "Pitted keratolysis".)

DIAGNOSIS — The diagnosis of trichomycosis is usually rendered clinically.

●Physical examination – Findings that strongly support this diagnosis include soft; yellow-white, red, or black; irregular masses attached to hair shafts, particularly when located in the axilla or pubic region. Patients may be unaware of the infection or present with a complaint of texture change of the hair or malodor.

Findings that should prompt consideration of other disorders include involvement of nonintertriginous sites and hair with adherent, firm, immobile structures (table 1). (See 'Differential diagnosis' below.)

●Supplementary diagnostic techniques – Although not typically necessary, dermoscopy, Wood's light examination, potassium hydroxide preparation, Gram stain, or bacterial culture can provide additional support for the diagnosis through demonstrating expected findings.

•Dermoscopy – Typical dermoscopic findings are irregular, golden yellow to pale yellow-white accretions adherent along the entire length of hair shafts, some with a brush-like, flame, skewer, or feathery appearance (picture 2A) [12]. (See 'Differential diagnosis' below and "Overview of dermoscopy of the hair and scalp", section on 'Abnormal dermoscopic patterns'.)

•Wood's light examination – Wood's light examination often reveals faint to bright yellow-white or yellow-green fluorescence [13-15]. (See "Office-based dermatologic diagnostic procedures", section on 'Wood's lamp examination (black light)'.)

•Potassium hydroxide preparation – A potassium hydroxide preparation of an involved hair shaft will show opaque, sheath-like structures surrounding the hair shaft [16]. (See 'Differential diagnosis' below.)

•Gram stain and culture – Laboratory tests to identify bacteria can confirm the diagnosis but are not necessary. Gram stain of affected hair will show hair shafts heavily colonized with gram-positive coccobacillary structures. Corynebacteria can be cultured on brain-heart infusion agar or chocolate-blood agar and identified with biochemical testing. (See "Approach to Gram stain and culture results in the microbiology laboratory".)

Examination of trichomycosis with reflectance confocal microscopy, a less widely available technique for in vivo microscopy, reveals lobulated structures with heterogenous refractility attached to the hair shaft [17]. In addition, bright yellow-green luminescence has been reported with ultraviolet-induced fluorescence dermoscopy [18].

DIFFERENTIAL DIAGNOSIS — Trichomycosis should be distinguished from piedra and pediculosis (table 1). Hair examination using dermoscopy facilitates diagnosis, differentiating pseudonits of trichomycosis and piedra from true nits of pediculosis and, thus, preventing possible unnecessary treatment, anxiety, and/or embarrassment (picture 2A-C) [19].

●Piedra – Piedra is an asymptomatic fungal infection of the hair shaft that is also known as trichomycosis nodularis [20-22].

•White piedra – White piedra typically manifests as white to beige, soft nodules or sheaths that are loosely adhered to hair shafts on the face, axillae, or genitals (picture 3). Nodules and sheaths of white piedra tend to be more discrete and well defined than trichomycosis and lack a creamy appearance.

Multiple Trichosporon species have been implicated in white piedra [20-23]. Faint Wood's light fluorescence is occasionally noted but may reflect the concomitant presence of bacteria. (See "Piedra" and "Infections due to Trichosporon species and Blastoschizomyces capitatus (Saprochaete capitata)".)

•Black piedra – Black piedra is caused by Piedraia hortae and should be distinguished from the nigra variant of trichomycosis. Black piedra classically presents with hard, firmly attached, brown to black nodules in contrast to the soft, creamy sheaths of trichomycosis (picture 4). Unlike trichomycosis, black piedra most often occurs on scalp hair. (See "Piedra".)

A potassium hydroxide preparation of hair shaft nodules will demonstrate fungal forms and is useful for confirming a diagnosis of piedra (picture 5A-B). (See "Office-based dermatologic diagnostic procedures", section on 'Potassium hydroxide preparation'.)

●Pediculosis – Patients with pediculosis capitis or pediculosis pubis present with tiny, nonmobile, oval eggs on hair shafts, sometimes yellowish in coloration (picture 6A-B) [24-26]. Adult lice and nymphs may also be visualized (picture 7).

Unlike trichomycosis, pruritus is a characteristic feature. Dermoscopic or microscopic examination of hair shafts aids in confirming the presence of nits (picture 2B-D). (See "Pediculosis capitis" and "Pediculosis pubis and pediculosis ciliaris".)

TREATMENT — Many patients desire treatment because of the abnormal appearance of hair and malodor associated with this condition. In the absence of treatment, the infection tends to persist.

Overview — Data on treatment options for trichomycosis are limited. Randomized trials have not been performed, and evidence for treatment efficacy is primarily limited to case reports, case series, and expert opinion.

Typical treatments include shaving of hair in the affected area and topical antimicrobial agents. Shaving should be sufficient but is often combined with topical antimicrobial therapy in an attempt to augment efficacy and reduce risk for recurrence. Topical antimicrobial therapy alone may also be sufficient [27].

Common choices for topical antimicrobial therapy include sulfur soap, benzoyl peroxide, erythromycin, clindamycin, and fusidic acid [1,27,28]. In addition, resolution of trichomycosis pubis with naftifine hydrochloride 1% cream, an antifungal agent with concomitant antibacterial properties, has been reported [29].

Our approach — Our preferred therapeutic approach consists of both of the following measures:

●Patients bathe daily and shave hair in affected area daily for two to three weeks.

●Patients wash the affected area daily with sulfur soap or apply a topical antimicrobial agent (eg, benzoyl peroxide 5%, erythromycin 2%, clindamycin 1%) once to twice daily.

For patients who comply with shaving, we suggest continuing topical antimicrobial therapy for one week. A typical treatment course for patients who do not shave the affected area is two to four weeks [27]; for these patients, we suggest continuing antimicrobial therapy for at least three days after visible signs of trichomycosis disappear.

Treatment is usually successful, leading to resolution of the characteristic nodules and sheaths on hair shafts by the end of treatment. Resolution of associated odor usually occurs within a few weeks.

INDICATIONS FOR REFERRAL — Apparent treatment failure (ie, persistence or rapid recurrence of clinical findings) warrants assessment for adherence to therapy and accuracy of the diagnosis. If the cause of treatment failure remains uncertain, referral to a dermatologist may be helpful.

PREVENTION — Methods that may reduce risk for recurrence of trichomycosis include good hygiene, regular shaving of hair in affected areas, control of hyperhidrosis, and weight loss. (See 'Epidemiology and risk factors' above.)

SUMMARY AND RECOMMENDATIONS

●Epidemiology and risk factors – Trichomycosis is a corynebacterial infection of hair shafts. Predisposing factors include poor hygiene, hyperhidrosis, and obesity. The infection is most common in young males. (See 'Microbiology' above and 'Epidemiology and risk factors' above.)

●Clinical presentation – Characteristic clinical findings in trichomycosis are creamy, opaque, soft nodules and sheath-like structures on hair shafts (picture 1A-C). The color is typically yellow-white and occasionally red or black. Odor is often present. Pain and pruritus are typically absent. (See 'Clinical presentation' above.)

●Diagnosis – Trichomycosis can be diagnosed based upon recognition of the characteristic clinical findings during a physical examination. The differential diagnosis includes other causes of hair shaft nodules or sheaths (table 1). In challenging cases, additional studies may be helpful for confirming the diagnosis and ruling out other conditions. (See 'Diagnosis' above.)

●Treatment – Data on the treatment of trichomycosis are limited.

•Selection – We suggest treating trichomycosis with a combination of shaving of hair in the affected area and application of a topical antimicrobial agent with activity against Corynebacterium species (Grade 2C). In our opinion, this approach may augment efficacy and reduce risk for recurrence. However, superiority of combination therapy has not been proven, and treatment with shaving alone or topical antimicrobial therapy alone is a reasonable alternative. Examples of reasonable choices for topical antimicrobial therapy include sulfur soap, benzoyl peroxide, erythromycin, and clindamycin. (See 'Treatment' above.)

•Duration – Hair should be shaved for two to three weeks. A reasonable duration for topical antimicrobial therapy is one week when used in conjunction with shaving; without shaving, the topical antimicrobial agents can be applied for two to three weeks. (See 'Our approach' above.)

•Outcome – Treatment of trichomycosis is usually successful. Treatment failure may indicate poor adherence to therapy or an incorrect diagnosis. (See 'Indications for referral' above.)

●Prevention – Good hygiene practices and regular shaving of affected hair may help to reduce risk for recurrence of trichomycosis. (See 'Prevention' above.)