Chapter 68. Ainhum and Pseudoainhum

Constricting bands are classified as ainhum and pseudoainhum. Ainhum describes the development of constricting bands around toes in underdeveloped countries of Africa and may ultimately result in autoamputation. In the African Yorub language, ainhum means “to saw” or “file” and in the Brazilian patois, it means “fissure.” In the remainder of the world, constricting bands that mimic ainhum are termed pseudoainhum.

Ainhum (dactylolysis spontanea) is traditionally a disease of middle-aged African males accustomed to going barefoot.1 In the tropic and subtropic climates, its incidence has been reported as between 0.015% and 2% of the population.2 This same condition is rarely seen throughout the rest of the world. Occasional isolated cases were reported in the United Kingdom and North America.1,3 Pseudoainhum of all types is very rare.

The pathogenesis of ainhum has not been clearly elucidated. Chronic trauma, infection, hyperkeratosis, decreased vascular supply, and impaired sensation may produce excessive fibroplasia in a susceptible host.4 Dent et al described impaired blood supply to the foot proximal to the groove at the plantar digital junction. Poor perfusion was the result of attenuation of the posterior tibial artery and absence of the plantar arterial arch leading to abnormal healing following mechanical trauma. Ainhum has also been blamed on rotational stress applied to the bare, mechanically unstable foot.5

There are three pathophysiological categories of pseudoainhum: (1) congenital constricting bands are caused by the umbilical cord; (2) constriction by external forces, such as hairs or threads, which are generally factitial; and (3) constricting bands secondary to other diseases. These may be hereditary or nonhereditary. Hereditary causes include pachyonychia congenita, Mal de Meleda, mutilating keratoderma,6 lamellar ichthyosis,7 and psoriasis.8–10 Nonhereditary diseases include vascular anomalies as seen in Raynaud disease, diabetes mellitus, linear scleroderma, systemic sclerosis. Sensory changes associated with leprosy, tertiary syphilis, syringomyelia, and spinal cord tumors as well as trauma resulting in scar formation from burns, frostbite, and physical trauma can also cause constricting bands to form. When associated with chronic trauma and infection of the extremities, the pathophysiology may be identical to true ainhum.

Ainhum usually affects the fifth toe; it may be unilateral, but 75% of the cases are bilateral. One or more digits can be involved. All toes can be involved, even the great toe.11 In early lesions, a groove or sulcus appears at the plantar junction of the toe and the sole. As this sulcus deepens, edema develops distally and roentgenographic examination shows resorption of the underlying bone and ultimately autoamputation.12

Congenital constricting bands (Streeter bands) usually involve more than one part of the body (Fig. 68-1) and frequently encircle large structures such as limbs or even the trunk. They persist throughout life and interfere with normal growth of the involved segment unless surgically treated13 (Fig. 68-2). Autoamputation can occur. More than 50% of cases are associated with other congenital anomalies usually syndactyly or clubfoot when constricting bands are found on the feet.14

Factitious pseudoainhum may prove to be a most challenging diagnosis. Strands of hair, fibers, or threads are intentionally wrapped around digits or other body parts such as a nipple or penis. This phenomenon is most commonly encountered in children, but can occur in mentally ill adults.15 Because of soft-tissue swelling, the ligating band may not be visible and the true cause of the condition may not be immediately recognized.15

Acquired constricting bands are associated with a variety of medical and dermatological conditions. In general, pseudoainhum is more likely to involve any of the toes or even the hands (Fig. 68-3; eFig. 68-3.1). In children, when chronic dermatophyte infection is identified and appropriately treated, complete reversal of the constriction may occur. Severe hyperkeratosis as occurs with Vohwinkel syndrome (keratoderma hereditarium mutilans)6,16 may show constricting bands due to palmar and plantar hyperkeratoses as well as starfish-like and linear keratoses.

The pathology of ainhum and pseudoainhum are similar with fibrotic bands resembling scar tissue.4,12 The bands in ainhum usually extend deep into the subcutaneous layers and may impinge upon underlying skeletal and vascular structures. Additionally, moderate inflammation and epidermal or verrucous hyperplasia may be present. In pseudoainhum the bands tend to be more superficial. Also, in pseudoainhum there may be histologic clues to the associated disorder, such as dermatophytosis, foreign bodies, or distinct patterns of keratinization.

The constricting bands of both ainhum and pseudoainhum ultimately produce a dangling, twisted digit, which can become gangrenous or infected. When this tenuous connection produces necrosis, autoamputation occurs.

Diseases caused by constricting bands proceed slowly and often painfully over many years eventuating in autoamputation in severe cases.

Surgery is the mainstay of therapy and early intervention is important. In most cases of ainhum, prompt amputation may allow the patient to escape pain and infection. Early cases of ainhum or pseudoainhum may respond to conservative plastic repair with a Z-plasty or similar relaxing closure by avoiding further disease progression and damage to underlying structures.12

Impending amputation in Vohwinkel syndrome can sometimes be aborted by therapy with oral etretinate.16 When chronic fungal or bacterial infections or psoriasis are diagnosed in the early phase of band formation, treatment may reverse the threat to the digit (eFig. 68-3.2). Other predisposing causes of underlying diseases should be treated aggressively in the hope of forestalling progression. For example, a case of infantile psoriasis with pseudoainhum was successfully treated with narrowband UVB phototherapy and pimecrolimus.17

Ainhum is rarely seen in people who are protected by wearing shoes. Congenital pseudoainhum cannot be prevented. Psychological counseling may prevent recurrences of pseudoainhum in patients with factitial disease. Control of the underlying disease process may delay progression or prevent recurrence in pseudoainhum of the acquired type.