Pressure Alopecia

Pressure alopecia is localised hair loss at a site of prolonged pressure on the scalp, usually from lying in one position on a hard surface for hours. It is most often seen after long operations and in neonates.

Postoperative (pressure induced) alopecia follows surgery longer than 4 hours, especially cardiac surgery or operations with hypotension and hypothermia, and appears 3 to 28 days after surgery. Neonatal occipital alopecia follows the first weeks of life on the back of the head. It also occurs in people who are bedridden or unconscious.

The hair loss is usually temporary. If pressure causes ulceration, scarring leads to permanent loss.

Pathophysiology.

Pressure on the scalp causes ischaemia of hair follicles, which leads to follicle damage and then loss of hair (anagen arrest) in the area. Hypotension, hypothermia and vasoconstrictor drugs add to the ischaemia.

In neonates, the loss reflects friction and a physiological change from anagen to telogen hair in the first months of life.

• A sharply defined, oval or round patch of hair loss over the occiput or other contact site, appearing 1 to 4 weeks after the pressure.
• The skin may be normal, or show erythema, tenderness, a crusted ulcer or a scarred, shiny area.
• In neonates, a band of thin hair across the occiput that grows back over months.

Red flags.

• Ulceration, necrosis or signs of infection at the pressure site.
• No regrowth after 6 months, which suggests scarring.

• Clinical diagnosis from the history of prolonged immobility, surgery or hospital stay and the site of the patch.
• Trichoscopy shows broken hairs, black dots and yellow dots, with no scarring features in non-scarring cases.
• Biopsy only if scarring is suspected or the cause is uncertain.

Differential diagnosis.

• Alopecia areata, tinea capitis (fungal culture), trichotillomania and traction alopecia.
• Telogen effluvium (diffuse), aplasia cutis congenita and cicatricial alopecias.
• Syphilitic alopecia and discoid lupus erythematosus.

• Reassure the patient that non-scarring loss usually regrows within 1 to 3 months, and sometimes up to 6 months.
• Prevention during surgery: pad the head with a soft support, turn the head every 30 minutes where possible, and avoid hypotension. In bedridden patients, change position every 2 hours and use pressure relieving surfaces.
• Ulcers need wound care and pressure relief, with antibiotics for infection. Scarring alopecia may need excision or hair transplantation later.
• Topical minoxidil 5% has been used to hasten regrowth, though proof of benefit is limited.

Monitoring. Review at 3 and 6 months for regrowth.

Referral and escalation. Dermatology if there is no regrowth by 6 months, an ulcer or diagnostic doubt.