Pachyonychia Congenita Affecting Only the Nails

To the Editor: Pachyonychia congenita (PC) is a rare heritable disorder ®rst described by Jadassohn and Lewandowsky in 1906 (1). Nail changes that a€ect all the nails symmetrically are a hallmark of the disease. On the basis of the presence and prevalence of associated symptoms, numerous subdivisions of PC have been suggested. Both autosomal dominant and autosomal recessive forms have been described, re ̄ecting heterogeneity (2). We describe a patient with nail changes in the absence of other syndrome abnormalities, indicating that the coexistence of associated symptoms is not an absolute prerequisite for the diagnosis of PC, as has been reported in the past (3,4). A 3-month-old boy presented with a history of an enlarged head and nail dis®gurement since birth. There was no history of similar nail changes in any other member of the family in two generations and the parents were nonconsanguineous. On examination, most nails had wedge-shaped thickening and discoloration of the nail plate (Fig. 1).Noother abnormalitywas detected on mucocutaneous examination. Potassium hydroxide (KOH) examination and fungal culture were negative. Head circumference was increased, with prominent fontanelles. Computed tomography (CT) scan of the head revealed obstructive hydrocephalus due to aqueductal stenosis. Although there were no associated abnormalities as described with PC, the nail ®ndings were characteristic of this rare disorder. Abnormalities of the nails are the most consistent clinical ®ndings of this syndrome. A purely clinical classi®cation does not correlate satisfactorily with the observed phenotypic expression of all cases and recent biologic ®ndings also throw doubt on the accuracy of such a clinical classi®cation (5). The diagnostic clinical feature of PC is the presence of thickened wedgeshaped nails, but other clinical characteristics such as palmoplantar hyperkeratosis, localized foot blistering, follicular hyperkeratosis, mucosal leukokeratosis, and natal teeth are present in a variable number of patients (2). Wedge-shaped, thickened nails are the diagnostic clinical feature of PC. The proximal portions are smooth and normally attached to the lateral nail folds. The distal portion may increase to six times the normal thickness, producing a subungual keratinous mass that pushes the nail plate upward, arching it transversally, folding it longitudinally, and elevating it distally. The nails are commonly shed and regrowwith similar but more severe changes. Projections from the nail beds make the nails susceptible to trauma with consequent chronic paronychial infections.The extent ofmutation in the highly conserved 1A domain of K6, K16, andK17 is associatedwith various abnormalities associatedwith the syndrome.Theprominentnail involvementofPCre ̄ects the extensive expression of K6, K16, and K17 in the nail matrix (5). Isolated nail involvement in the absence of other abnormalities has been reported in the past in two families (3,4). The nail changes present in our patient are characteristic of PC, although associated ®ndings of the syndrome are lacking. Our patient appears to represent a monosymptomatic form of PC. The variable degree of gene mutation involving K6, K16, and K17 or predominantly a particular keratin may result in nail abnormalities alone. Perhaps it may represent a di€erent allele, resulting in a milder phenotype. The presence of congenital hydrocephalus may be another new association of pachyonychia congenita ormay just be a chance occurrence.