Psoriasis presents with isolated nail involvement in about 5-10% of patients. 11, 12

The commonest clinical presentation of psoriasis was pitting of the nail plate, followed by subungual hyperkeratosis as seen in Figure 2a.

The most common histological change observed in our study was parakeratosis of the nail plate (n=19), followed by acanthosis of nail base (n=15) and nail matrix (n=5). Hypergranulosis of nail base was noted in 7 cases. [Figure 2a] Spongiosis and neutrophilic infiltration in the nail base epithelium were also seen in 3 cases. [Table 2]

Figure 2

Table 2

Histopathologic features	Number of cases	Percentage (%)
Parakeratosis	19	100
Fragmentation of nail plate	11	58
Plasma crusting	3	16
Acanthosis of nail base	15	79
Hypergranulosis	7	37
Acanthosis of nail matrix	5	26
Spongiosis	3	16

Most of the microscopic findings in our study were in concordance with the study by Grover C et al and Dogra A. ¹¹

In our study, onychomycosis was the second most common disease comprising 24% of all biopsies. Discoloration of the nail plate was the common clinical finding observed in our patients. [Figure 3a]

PAS staining is reported as the most sensitive method for the detection of hyphae in the nail unit (sensitivity 82%), compared to culture (sensitivity 53 %), direct microscopy with KOH (sensitivity 48%) and fluorescence brightener (sensitivity,53%).2, 5, 13, 14, 15, 16, 17, 18

The most common microscopic finding was fragmentation of the nail plate (n=11). [Figure 3b] Parakeratosis was seen in 5 cases and hyperkeratosis in one case. Acanthosis of the nail base epithelium was seen in 5 cases in our study. 2 cases showed hypergranulosis. There were no significant changes in the nail matrix. While 3 cases showed inflammatory infiltrate in the subungual tissue. [Table 3]

Figure 3

Table 3

Histopathologic features	Number of cases	Percentage (%)
Parakeratosis	5	41
Fragmentation of nail plate	10	91
Plasma crusting	2	17
Acanthosis of nail base	5	41
Hypergranulosis	2	16
Acanthosis of nail matrix	1	8
Spongiosis	2	17
Fungal organisms	12	100

In all the cases, PAS staining revealed the invasion of the nail unit by fungal hyphae. [Figure 3c] Overall, the presence of fungal hyphae on histology complemented by PAS staining was helpful in the diagnosis of onychomycosis in our study.

Grover C et al studied histology in onychomycosis in 15 patients using PAS staining and reported presence of fungal hyphae in 14 patients (93.3%). They also observed hyperkeratosis, parakeratosis, hemorrhage and serum crusts in the nail unit.18

Lichen planus limited to the nails is uncommon. It is seen in 1-10% of cases of disseminated lichen planus.2, 19, 6, 13, 14

4 out of 5 patients with lichen planus presented with pterygium of the nails which is the characteristic clinical finding as seen in a study by Tosti et al. ¹⁹ [Figure 4a] The characteristic microscopic findings noted in our study were fragmentation of the nail plate (n=3), hypergranulosis (n=3) and acanthosis (n=3) of the nail base combined with inflammatory infiltrate in the subungual tissue. 2 cases also showed civatte bodies in the nail base epithelium and basal cell vacuolar degeneration. [Figure 4b] The nail matrix was unremarkable in 4 out of 5 cases. [Table 4]

Figure 4

Table 4

Histopathological features	Number of cases (n=5)	Percentage (%)
Inflammatory infiltrate	5	100
Fragmentation of nail plate	3	60
Parakeratosis	1	20
Acanthosis of nail base	3	60
Hypergranulosis	3	60
Civette bodies	2	40
Basal cell vacuolar change	2	40

There are very few studies on histopathology of lichen planus of the nails. Few of which include studies by Flores et al, Martin B and Grover et al. 2, 5, 14, 20 They have quoted that lichen planus of nails show similar features as skin which includes hypergranulosis, acanthosis, presence of civatte bodies and basal cell vacuolar degeneration. However exclusive features limited to the nails are parakeratosis, spongiosis and mild inflammation 2, 5, 14 which were also seen in our study.

The causes of abnormal pigmentation are numerous, including inflammation, physiological longitudinal melanonychia, trauma, drugs and several systemic disorders. 13 Moreover, nail biopsy is of specific use to rule out malignant melanoma of the nails.

All the cases which presented with pigmented bands clinically had melanoma as one of their clinical differentials. Hence, nail biopsy was of value to rule out melanoma in our study.

Either diffuse or focal pigmentation of the nail plate was observed both grossly and microscopically in all the 7 cases. 3 cases in addition had pigment deposits in the nail base. [Figure 5 a, b]

Figure 5

Between 10% - 66% of patients with alopecia areata have nail involvement. The nail changes may precede or follow the onset of alopecia. 21 Pitting of the nail plate was the presenting feature in two out of 3 cases of alopecia areata seen in our study. [Figure 6a]

Nails are targeted by the same type of inflammatory cells that target hair follicles in alopecia areata.

Characteristic microscopic nail changes in alopecia areata include lymphocytic infiltration and spongiotic vesiculation in the nail base epithelium. 22

The prominent microscopic changes observed in all the 3 cases were parakeratosis and plasma crusting of the nail plate with inflammatory infiltrate in the subungual tissue. [Figure 6b]

Figure 6

Histopathological analysis of the nail unit provides a wealth of information for diagnosing various nail disorders and to determine their pathogenesis and prognosis. Histopathological features and diagnostic criteria are available in the literature which needs to be utilised in interpreting the nail lesions. Though nail biopsies are not performed routinely, it gives a definitive rather than a hypothetical approach to treatment, especially in clinically ambiguous conditions.