In APL, the proximal and outer root sheath of hair follicles undergoes apoptosis and disintegration at the end of the anagen phase. Patients are born with scalp and body hair but develop irreversible hair loss beginning at a few months of age, with a frontal to posterior progression on the scalp. In some cases, patients are born hairless. Papular lesions erupt within the first year of life, most prominently under the midline of the eye, face, and extremities. Papular lesions are made of keratin cysts associated with malformation of the pilosebaceous system.
Q84.0 – Congenital alopecia
403798006 – Atrichia congenita
Differential Diagnosis & Pitfalls
- Hereditary vitamin D-dependent rickets type 2A – An autosomal recessive disorder with gene mutations of vitamin D receptor. Patients have clinical and histopathological features identical to APL, ie, irreversible hair loss and papular lesions. These patients are distinguished by hypocalcemia, hypophosphatemia, normal calcidiol (25-hydroxyvitamin D) and elevated calcitriol (1,25-dihydroxyvitamin D3) levels, elevated alkaline phosphatase, hyperparathyroidism, osteomalacia, and rickets. Patients respond to supplementation with calcitriol and calcium.
- Alopecia universalis (see alopecia areata) – Alopecia with variable onset and possible reversal. Trichoscopy may show "yellow dots" (hyperkeratotic plugs), micro-exclamation mark hairs, and "black dots" (destroyed hairs in follicle opening). There are no papular lesions. Patients may respond to systemic treatments.
- Oral-facial-digital syndrome – An X-linked dominant ectodermal dysplastic syndrome with congenital papular lesions and hypotrichosis. Patients also present with cleft lip / palate, hypoplastic alae nasi, brachydactyly, and intellectual disability and are at risk for polycystic kidney disease.
- Schöpf-Schulz-Passarge syndrome – An ectodermal dysplasia of unknown inheritance with congenital papular lesions and hypotrichosis. Patients are known for developing palmoplantar keratoderma, hypodontia, furrowed nails, and multiple eyelid apocrine hidrocystoma.
- Generalized basaloid follicular hamartoma syndrome – An autosomal dominant disease with congenital or early-onset pigmented papular lesions and hypotrichosis. Patients also have palmoplantar pits, follicular hamartomas, comedones, and acrochordons and are at risk for basal cell carcinoma, systemic lupus erythematosus, antiphospholipid antibody syndrome, cystic fibrosis, and/or myasthenia gravis.
- Bazex-Dupré-Christol syndrome – An X-linked dominant disease with congenital hypotrichosis and early-onset papular lesions. Patients also present with follicular atrophoderma, comedones, hidradenitis suppurativa, hair shaft anomaly (eg, trichoepithelioma), and basal cell carcinoma.
- Rombo syndrome – An autosomal dominant disease with late-onset hypotrichosis and papular lesions beginning at about 7-10 years of age. Patients also present with vermiculate atrophoderma, peripheral vasodilatation, telangiectasia, trichoepithelioma, and basal cell carcinoma.