A case of follicular keratosis with trichostasis on an amputated limb

A 29-year-old woman was referred to the Center for Rehabilitation, with complaints of pain and loss of mobility of the stump of her left leg. In 1999, she had undergone a transfemoral amputation because of complex regional pain syndrome (CRPS) type 1 of her left lower limb. At the time of her presentation in 2003, she had no signs of CRPS type 1, as described by the International Association for the Study of Pain, on the stump. She did not wear a prosthesis or clothing over the amputated side, because of persistent touch-evoked pain. She was not able to notice warm or cold sensations with the stump, and it is unknown for how long this had existed. She ambulated by using crutches and a wheelchair. Physical examination showed an obese woman with a giant transfemoral stump with a surplus of soft tissue. The stump felt cold. The distal part of the stump showed a circumscript asymptomatic area consisting of multiple hyperkeratotic follicular papules and hyperpigmentation (Fig. 1). This skin condition was not present prior to amputation. Potassium-hydroxide preparations and cultures for fungus and bacteria were negative. Vascular examination by Doppler ultrasound showed no major abnormalities in the blood flow of the stump. A skin biopsy taken from the affected area was not representative, showing only dermal oedema. Physical examination 3 months later revealed erythema on the stump with a circumscript field of large yellowish brown keratotic papules with follicular distribution (Fig. 1, inset). Histopathological examination of a second biopsy showed a very wide distended follicle containing a keratotic plug consisting of laminated and amorphous keratin containing several vellus hairs in a bundle (double refractile with polarization). The follicular wall matured normally. The histopathological diagnosis was compatible with follicular keratosis with trichostasis (Fig. 2). In order to enhance mobility, partial distal resection of the stump, including the affected skin, was performed. Over the following 6 months, the new stump with unaffected skin returned to the situation prior to surgery, i.e. follicular hyperkeratosis. Complaints of touch-evoked pain did not improve after resection, and mobility of the stump was not enhanced. A third biopsy of the affected area of the stump again showed a distended follicle containing several vellus hairs and follicular plugging, but also extrafollicular vellus hairs evoking a foreign-body cell reaction. Follicular keratosis of amputated sites is not uncommon and is confined to sites with continuous friction caused by an ill-fitting prosthesis. Unlike the cases described by Ibbotson et al., 2 our patient never used a prosthesis, owing to touch-evoked pain of the stump, thereby excluding friction as cause of the skin condition. The condition in our patient could be classified as follicular keratosis with secondary vellus hair retention caused by the hyperkeratotic plug. Retention of vellus hairs is named trichostasis. Trichostasis spinulosa is a not uncommon skin disorder that presents as follicular keratosis, but we prefer to use the diagnosis follicular keratosis with trichostasis for our patient, as large yellowish-brown, asymptomatic, hyperkeratotic papules were observed, whereas in trichostasis, mildly pruritic and elevated, raspy, spinous, follicular plugs are most freqently seen. Trichostasis results from successive production of vellus telogen club hairs from a single hair matrix in a follicle. There are several speculations regarding the aetiology of damage to hair follicles, such as external irritants or development of numerous resting buds in response to an unknown stimulus. There are two types of trichostasis spinulosa: the classical type with nonitching, solitary Figure 1 Transfemoral stump with large circumscribed follicular keratotic papules. Inset: close-up view. Figure 2 Skin histology shows a distented follicle with a horny plug with many cross-sections of vellus hairs. The superficial dermis shows a very mild perivascular lymphocytic inflammatory infiltrate (haematoxylin and eosin, original magnification · 4).