Pili annulati with fragility: Electron microscopic findings of a case.

Pili annulati (PA) is typically characterized by shinny beads seen along the hair shaft. PA is accepted to belong to the classification of hair shaft abnormalities without fragility. Herein, we described a 14-year-old, fair skin with dark-haired girl diagnosed as PA with fragility which was demonstrated by weathering features in electron microscopic examinations. The patient had shinny beaded, easily breakable hairs since the age of four. A few broken hairs were observed by a light pull test. Transmitted light microscopy revealed periodic dark bands in the hair shaft. These dark bands disappeared after application of 10% aqueous potassium hydroxide. Multiple cavities within hair shaft and severe cuticular damages representing the weathering pattern were observed in electron microscopic examinations. All these findings were found to be consistent with presence of fragility in PA. This case provides evidences of fragile hair structure of PA which may be due to pathological cavities within hair shafts.

INTRODUCTION

Pili annulati (PA) is a rare hair shaft abnormality, characterized by shinny beads seen along the hair shaft. These beads reversely correspond to the alternating dark bands among light bands under transmitted light microscopy.[1] Since PA was first described by Landois in 1866,[1] only about 50 cases with PA has been published. The pathogenesis of PA has not been clearly established yet. PA is considered to be autosomal dominantly inherited hair shaft disorder, but sporadic cases have also been reported.[2] It can present at birth, during infancy, or after age of two. PA may be firstly obvious after puberty or in adulthood.[34] Although the scalp has been mostly reported to be affected, pubic,[5] beard,[6] and axillary hairs[7] have been also reported to be involved. The abnormalities of PA become more noticeable with age, in contrast to fragility-associated disorders, in which fragility becomes subtle with puberty.[8]

Although PA was categorized in hair shaft abnormalities without fragility, two patients were shown to have fragile hairs corresponding to weathered hair structure due to internal weakness of the shaft caused by pathological cavities.[9] In this report, we described a girl diagnosed as PA with fragility and demonstrated the weathering features in electron microscopic examinations. This case provides additional evidences of fragile hair structure of PA which were suggested in only a small number of patients.

CASE REPORT

A 14-year-old, fair skinned, dark-haired Causation girl was presented with shinny beaded, easily breakable hairs since she was four [Figure 1]. Hairs were only cosmetically disturbing for the patient and her family. There was no history of any trauma, shedding, or alopecia. Her parents were nonconsanguineous. Her mother had had similar hairs during her childhood and adolescence, which improved as she got older. The other family members were not available for examination. The axillary and pubic hairs were normal. On examination, a few broken hairs came to hand by a light pull test. Transmitted light microscopy revealed periodic dark bands in the hair shaft [Figure 2], which diminished toward to the end of hair. The otherwise dermatological and systemic examinations were normal.

Figure 1

Shinny beading along the hair shafts

Figure 2

Periodic dark bands in the hair shaft under transmitted light microscopy

Under light microscopy, the hair samples within normal medium [Figure 3a] were then embedded in 10% aqueous potassium hydroxide. The dark bands disappeared after 6 minutes and homogeneous color along hair shaft was achieved [Figure 3b]. Upon this observation, these bands were considered as pathological cavities in hair structure, not normal medulla bands.

Figure 3

(a) Dark cavities seen within normal medium disappeared (b) after 6 minutes of embedding in 10% aqueous potassium hydroxide medium under light microscopy

To perform electron microscopic examinations, the hair samples of the patient were mounted on stubs and sputter coated with gold paladium. Then they were examined with a scanning and transmission electron microscope (JEM 1200EX, Jeol, Tokyo, Japan). Transmission electron microscopy (TEM) of the hair samples demonstrated various sizes of multiple cavities within cuticular and cortical cells and indentations adjacent to these cavities [Figure 4a and b]. Scanning electron microscopic examination (SEM) provided observations of various severe cuticular damages corresponding to the localizations of cavities [Figures 5a–d]. In contrast, the unaffected hairs had normal hair structure.

Figure 4

Transmission electron microscopy showed (a) multiple cavities between cuticular and cortical cells and (b) indentations of undamaged cuticle adjacent to cavities (arrowed)

Figure 5a-d

Scanning electron micrographs of hair samples demonstrated damaged cuticle and cortex structures with various severities of changes adjacent to pathological cavities within hair shafts

Depending on these clinical features and light and electron microscopic findings, the patient was diagnosed as PA with fragility and weathered structure.

DISCUSSION

PA is clinically more noticeable in fair hairs than dark-haired patients as in this case, because less pigmented hairs transmit more light in transmitted light microscopy.[1] Light bands seen with naked eye were suggested to correspond to air-filled spaces[10] or proteinaceous materials.[1] They do not transmit the light under light microscopy and appear as dark pathological cavities located in the cortex of hair shaft that scatter the light.[5] The pigmented medulla should be differentiated since they may resemble dark bands when it is present intermittently. Medulla has rounded tips in contrast to tapering and sharp cavities in PA.[3] The disappearance of dark bands in 10% aqueous potassium hydroxide medium may be used to support the diagnosis of PA. The cuticular damage in PA hairs might have allowed the penetration of the medium into cavities or collapsing of the cavities leading the transmission of the light.[11]

Pseudopili annulati (PPA) is the main differential diagnosis for PA. It is a type of ringed hair with beads appearing upon transverse illumination because of the elliptical shape and twisting of the hair. The hair shaft of PPA is normal under transmitted light microscopy, TEM, and SEM, in contrast to PA. The hair fiber appears uniformly dark without banding; however, it shows variations in thickness causing repeated fusiform segments. PPA has not been shown to be related to any inheritance or associated with any other abnormality, unlike PA.[12] As seen in our case, clinical findings and light microscopic features did not demonstrate features of PPA.

The pathogenesis of PA has been explained depending on several mechanisms such as an underlying cytokeratin abnormality[1] or a matrix formation defect.[11] Several basal membrane zone components were demonstrated to be abnormally distributed.[2] A mutation in proteins involved in signaling and regulation of formation and degradation of the lamina densa and sublamina densa region might result in an abnormal assembly or remodeling of the basal membrane zone. PA was found unlikely to be attributable to an abnormality of any of the common known cytokeratins examined.[10] In 2004, a gene locus responsible for PA was mapped to chromosome 12q24.32-24.33. Because chromosome 12q locus does not contain structural genes related to the keratin genes, it is more likely that PA may be caused by a mutation in a regulatory gene affecting hair follicle cell proliferation or differentiation.[3]

The aminoacids of the hairs with PA demonstrated elevated lysine and decreased cysteine content. These findings may be parts of the responsible process contribute to fragility that has been suggested in some patients with PA,[11] although hair fragility has not been mentioned as a clinical feature of PA.[13] It is well known that abnormal hair structures are prone to excessive weathering than normal hair shafts due to underlying cavities within cortex leading to intrinsic shaft weakness. In SEM, the cuticle of the affected hair may seem to be intact but it has a cobblestoned appearance and fluted. Because of the multiple cavities within and around cortical cells, the cuticular cells may be thrown into these folds. In TEM, many abnormal cavities of varying spaces and sizes are observed within the cortex between cortical macrofibrils and within cortical cells. Beside these alterations, medulla remains intact and normal.[9] The electron microscopic findings of our patient were compatible with these features of PA. Besides, SEM demonstrated rare findings of weathering seen in PA as described in the report of Feldmann et al.[9] The nodes of PA might have weakened hair structure and breaks when exposed to physical trauma such as vigorous combing and environmental factors. Minor indentations as in our case might not cause breaks in hair shaft.

Although quantitative examinations of tensile breaking strength were within normal limits, vigorous combing, brushing of the hair, or cosmetic measures result in excessive weathering and structural damage associated with these pathological nodes in PA. Therefore, avoiding physical trauma, vigorous combing, cosmetic implementations were recommended to the present case to reduce fragility.

In conclusion, the diagnosis of PA needs careful clinical and microscopic examinations since it is asymptomatic and clinically less apparent in time. Although PA is generally classified in hair shaft disorders without fragility, some patients may have fragility due to pathological cavities within hair shafts.